OFFSHORE STANDARD
DNV-OS-H206
Loadout, transport and installation
of subsea objects
(VMO Standard - Part 2-6)
SEPTEMBER 2014
The electronic pdf version of this document found through http://www.dnv.com is the officially binding version
DET NORSKE VERITAS AS
FOREWORD
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to operate and a competitive advantage. Our core competence is to identify, assess, and advise on risk management. From
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and the environment.
DNV service documents consist of among others the following types of documents:
— Service Specifications. Procedural requirements.
— Standards. Technical requirements.
— Recommended Practices. Guidance.
The Standards and Recommended Practices are offered within the following areas:
A) Qualification, Quality and Safety Methodology
B) Materials Technology
C) Structures
D) Systems
E) Special Facilities
F) Pipelines and Risers
G) Asset Operation
H) Marine Operations
J) Cleaner Energy
O) Subsea Systems
U) Unconventional Oil & Gas
© Det Norske Veritas AS September 2014
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This service document has been prepared based on available knowledge, technology and/or information at the time of issuance of this document, and is believed to reflect the best of
contemporary technology. The use of this document by others than DNV is at the user's sole risk. DNV does not accept any liability or responsibility for loss or damages resulting from
any use of this document.
Offshore Standard DNV-OS-H206, September 2014
CHANGES – CURRENT – Page 3
CHANGES – CURRENT
General
This is a new document.
Det Norske Veritas AS, company registration number 945 748 931, has on 27th November 2013 changed its
name to DNV GL AS. For further information, see www.dnvgl.com. Any reference in this document to
“Det Norske Veritas AS” or “DNV” shall therefore also be a reference to “DNV GL AS”.
General
This is a new document in a series of documents replacing the DNV Rules for Planning and Execution of
Marine Operations (1996/2000); this standard replaces Pt.2 Ch.6. Extensive revisions and/or amendments have
been made, with the following main changes:
— Sec.2 General Requirements is new, combining new content with some original text from Section 4 of the
previous Rules.
— The simplified method for estimation of dynamic lift loads and relevant soil force/capacities is covered in
DNV-RP-H103 and the items covering these parts in section 2 and 3 in the Rules are hence omitted.
— Section 2 and 3 are now section 3 and 7 respectively and they have been considerably re-written.
— Three (3) new sections have been added:
1) Sec.4 Loadout and transport
2) Sec.5 Subsea lifting
3) Sec.6 Installation of pipelines, risers, cables and umbilicals.
DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
Contents – Page 4
CONTENTS
CHANGES – CURRENT ................................................................................................................... 3
1
Introduction ............................................................................................................................... 8
1.1
1.2
1.3
2
Application .................................................................................................................................................... 8
1.1.1 General ............................................................................................................................................... 8
1.1.2 Complementary standards ................................................................................................................. 8
1.1.3 Conditions for use .............................................................................................................................. 8
References....................................................................................................................................................... 8
1.2.1 Numbering and cross references ........................................................................................................ 8
Definitions..................................................................................................................................................... 10
1.3.1 Verbal forms..................................................................................................................................... 10
1.3.2 Terminology ..................................................................................................................................... 10
1.3.3 Abbreviations ................................................................................................................................... 10
1.3.4 Symbols............................................................................................................................................ 11
General requirements ............................................................................................................. 12
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
Planning ........................................................................................................................................................ 12
2.1.1 General ............................................................................................................................................. 12
2.1.2 Operation period............................................................................................................................... 12
2.1.3 Environmental conditions ................................................................................................................ 12
2.1.4 Critical design parameters................................................................................................................ 12
2.1.5 Installation site survey ..................................................................................................................... 13
2.1.6 Route survey..................................................................................................................................... 13
2.1.7 Risk management ............................................................................................................................. 13
Documentation ............................................................................................................................................. 13
2.2.1 General ............................................................................................................................................. 13
2.2.2 Design documentation...................................................................................................................... 13
2.2.3 Operation manual ............................................................................................................................. 14
Lifting appliances......................................................................................................................................... 14
2.3.1 Crane ................................................................................................................................................ 14
2.3.2 Other lifting appliances .................................................................................................................... 14
Load and motion limiting systems.............................................................................................................. 15
2.4.1 General ............................................................................................................................................. 15
2.4.2 Active heave compensation systems................................................................................................ 15
2.4.3 Passive heave compensation systems .............................................................................................. 16
Lifting equipment ........................................................................................................................................ 17
2.5.1 General ............................................................................................................................................ 17
2.5.2 Design considerations ...................................................................................................................... 17
2.5.3 Wet-storage of lifting equipment ..................................................................................................... 18
2.5.4 Custom-made lifting equipment....................................................................................................... 18
2.5.5 Lifting tools...................................................................................................................................... 18
2.5.6 Test lift ............................................................................................................................................. 18
Guiding and positioning systems ................................................................................................................ 19
2.6.1 General ............................................................................................................................................. 19
2.6.2 Control of lift.................................................................................................................................... 19
2.6.3 Guide lines/guide wires.................................................................................................................... 19
2.6.4 Bumpers and guides ......................................................................................................................... 19
Installation aids ............................................................................................................................................ 20
2.7.1 General ............................................................................................................................................. 20
2.7.2 Design considerations ...................................................................................................................... 20
2.7.3 Design factor .................................................................................................................................... 20
Miscellaneous systems ................................................................................................................................. 20
2.8.1 Dynamic positioning systems .......................................................................................................... 20
2.8.2 Ballasting systems............................................................................................................................ 21
2.8.3 Atmospheric diving systems ............................................................................................................ 21
ROV operations............................................................................................................................................ 22
2.9.1 Planning............................................................................................................................................ 22
2.9.2 Schedule and contingency................................................................................................................ 22
2.9.3 Maintenance and tests ...................................................................................................................... 22
2.9.4 ROV Tools ....................................................................................................................................... 23
2.9.5 Operation.......................................................................................................................................... 23
2.9.6 Navigation ........................................................................................................................................ 23
DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
Contents – Page 5
2.10
3
Loads and structural design ................................................................................................... 26
3.1
3.2
3.3
3.4
4
Loads ............................................................................................................................................................. 26
3.1.1 General ............................................................................................................................................. 26
3.1.2 Loadcases and analysis .................................................................................................................... 26
Vessel motions and accelerations................................................................................................................ 26
3.2.1 General ............................................................................................................................................. 26
3.2.2 Characteristic vessel motions generated by wind seas..................................................................... 27
3.2.3 Characteristic vessel motions generated by swell ............................................................................ 27
Loads ............................................................................................................................................................. 27
3.3.1 Weight and buoyancy....................................................................................................................... 27
3.3.2 Hydrostatic loads.............................................................................................................................. 27
3.3.3 Environmental loads......................................................................................................................... 28
3.3.4 Accidental loads ............................................................................................................................... 28
3.3.5 Pull-down and pull-in loads ............................................................................................................. 28
3.3.6 Off-lead, side-lead forces and horizontal offset ............................................................................... 28
3.3.7 Loads during positioning.................................................................................................................. 28
3.3.8 Other loads ....................................................................................................................................... 29
Structural design.......................................................................................................................................... 29
3.4.1 General ............................................................................................................................................. 29
3.4.2 Object ............................................................................................................................................... 29
3.4.3 Bumpers and Guides ........................................................................................................................ 29
3.4.4 Rigging lay down and securing........................................................................................................ 29
3.4.5 Seafastening and supporting structures ............................................................................................ 29
3.4.6 Inspection ......................................................................................................................................... 29
Loadout and transport ............................................................................................................ 31
4.1
4.2
4.3
4.4
4.5
5
2.9.7 Launching restrictions...................................................................................................................... 23
2.9.8 Monitoring........................................................................................................................................ 24
2.9.9 Deep water ROV operations ............................................................................................................ 24
Operational requirements........................................................................................................................... 24
2.10.1 Application ....................................................................................................................................... 24
2.10.2 Operation criteria ............................................................................................................................. 24
2.10.3 Pre-installation surveys ................................................................................................................... 25
2.10.4 Testing.............................................................................................................................................. 25
2.10.5 Organization .................................................................................................................................... 25
2.10.6 Safety and contingency .................................................................................................................... 25
General.......................................................................................................................................................... 31
4.1.1 Application ....................................................................................................................................... 31
Submerged towing ....................................................................................................................................... 31
4.2.1 General ............................................................................................................................................. 31
4.2.2 Submerged tow of objects attached to installation vessel ................................................................ 31
4.2.3 Submerged tow of objects attached to towed buoy.......................................................................... 31
4.2.4 Surface or sub-surface tow of long slender elements....................................................................... 32
4.2.5 Loads and analyses........................................................................................................................... 32
Bundles.......................................................................................................................................................... 32
4.3.1 General ............................................................................................................................................. 32
4.3.2 Load-out of bundles ......................................................................................................................... 33
4.3.3 Towing of bundles............................................................................................................................ 33
Pipelines, risers, cables and umbilicals ..................................................................................................... 34
4.4.1 General ............................................................................................................................................. 34
4.4.2 Load out by lifting............................................................................................................................ 34
4.4.3 Load-out by spooling ....................................................................................................................... 34
4.4.4 Sea transport..................................................................................................................................... 34
Pipe joints ..................................................................................................................................................... 35
4.5.1 General ............................................................................................................................................. 35
4.5.2 Load out by lifting............................................................................................................................ 35
4.5.3 Sea Transport ................................................................................................................................... 35
4.5.4 Offshore pipe loading....................................................................................................................... 35
Subsea lifting............................................................................................................................ 36
5.1
5.2
General.......................................................................................................................................................... 36
5.1.1 Application ....................................................................................................................................... 36
Loads and analysis ....................................................................................................................................... 36
5.2.1 Loads ................................................................................................................................................ 36
5.2.2 Combination of loads ...................................................................................................................... 36
DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
Contents – Page 6
5.3
5.4
5.5
5.6
5.7
6
Installation of pipelines, risers, cables and umbilicals ......................................................... 43
6.1
6.2
6.3
6.4
6.5
6.6
6.7
7
5.2.3 Lift analysis - General ...................................................................................................................... 36
5.2.4 Simplified method for estimation of hydrodynamic forces acting on submerged objects............... 37
Acceptance criteria ..................................................................................................................................... 38
5.3.1 Acceptance criteria – Simplified method ......................................................................................... 38
5.3.2 Acceptance criteria - Alternative .................................................................................................... 38
More accurate estimation of hydrodynamic forces .................................................................................. 39
5.4.1 General ............................................................................................................................................. 39
5.4.2 Documentation ................................................................................................................................. 39
Lifted object.................................................................................................................................................. 39
5.5.1 General ............................................................................................................................................. 39
5.5.2 Pipelines, risers, cables and umbilicals ............................................................................................ 40
5.5.3 Spools............................................................................................................................................... 40
5.5.4 Retrieval of damaged objects ........................................................................................................... 40
Operational aspects ..................................................................................................................................... 40
5.6.1 General ............................................................................................................................................. 40
5.6.2 Installation tolerances....................................................................................................................... 41
5.6.3 Wet parking ...................................................................................................................................... 41
5.6.4 Safety and contingency .................................................................................................................... 42
Deep water ................................................................................................................................................... 42
5.7.1 Deep water lowering operations....................................................................................................... 42
General.......................................................................................................................................................... 43
6.1.1 Application ....................................................................................................................................... 43
6.1.2 Risk management ............................................................................................................................. 43
Operational planning................................................................................................................................... 44
6.2.1 General ............................................................................................................................................. 44
6.2.2 Operation period............................................................................................................................... 44
6.2.3 Continuous operations...................................................................................................................... 44
6.2.4 Safety and contingency .................................................................................................................... 44
6.2.5 Operation manual ............................................................................................................................. 44
Installation spread, aids and ancillary equipment.................................................................................... 44
6.3.1 Installation spread ............................................................................................................................ 44
6.3.2 Calibration and testing .................................................................................................................... 45
6.3.3 Installation aids and ancillary equipment......................................................................................... 45
6.3.4 Abandonment and recovery system ................................................................................................. 45
6.3.5 In-line and termination structures .................................................................................................... 46
6.3.6 (Platform) Pull-in winch systems..................................................................................................... 46
Loads and design.......................................................................................................................................... 46
6.4.1 Loads ................................................................................................................................................ 46
6.4.2 Load effects ...................................................................................................................................... 47
6.4.3 Limit states ....................................................................................................................................... 47
6.4.4 Failure modes ................................................................................................................................... 47
Installation - General................................................................................................................................... 48
6.5.1 General ............................................................................................................................................. 48
6.5.2 Initiation .......................................................................................................................................... 48
6.5.3 Laying ............................................................................................................................................. 48
6.5.4 Lay monitoring................................................................................................................................. 48
6.5.5 Lay-down ......................................................................................................................................... 49
6.5.6 Shore pull ......................................................................................................................................... 49
Product specific installation requirements ................................................................................................ 50
6.6.1 Pipeline system installation.............................................................................................................. 50
6.6.2 Riser, umbilical and cable installation ............................................................................................. 50
6.6.3 J-tube pull-in of flexible risers, flexibles pipelines, umbilicals and cables ..................................... 50
6.6.4 Bundle and pipe string installation................................................................................................... 51
6.6.5 Tie-in of pipe strings and bundles ................................................................................................... 51
Tie-in operations .......................................................................................................................................... 51
6.7.1 Application ...................................................................................................................................... 51
6.7.2 General ............................................................................................................................................. 51
Soil and foundations ................................................................................................................ 52
7.1
Soil capacity and on bottom stability ......................................................................................................... 52
7.1.1 General ............................................................................................................................................. 52
7.1.2 Stability calculations ........................................................................................................................ 52
7.1.3 Material factors ................................................................................................................................ 52
DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
Contents – Page 7
7.2
7.3
Loads and installation aspects .................................................................................................................... 52
7.2.1 Positioning loads .............................................................................................................................. 52
7.2.2 Installation effects on the soil .......................................................................................................... 52
7.2.3 Penetration and levelling of skirted foundations.............................................................................. 53
Miscellaneous ............................................................................................................................................... 53
7.3.1 Effects of conductor installation and shallow well drilling ............................................................. 53
7.3.2 Retrieval of object ............................................................................................................................ 54
DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
Sec.1 Introduction – Page 8
SECTION 1 INTRODUCTION
1.1 Application
1.1.1 General
1.1.1.1 This standard, DNV-OS-H206 - Loadout, transport and installation of subsea objects, provides
requirements, recommendations and guidance for loadout, transport and installation of subsea objects.
1.1.1.2 The standard applies to subsea objects being lowered to their final position on the seabed by cranes or
other means, or pulled down or ballasted from the sea surface. Typical objects covered are subsea structures,
pipelines, umbilicals, bundles, cables and risers.
1.1.2 Complementary standards
1.1.2.1 DNV offshore standards covering marine operations, i.e. DNV-OS-H101, DNV-OS-H102 and DNVOS-H201 through DNV-OS-H206, are collectively referred to as the VMO Standard.
Guidance note:
The “VMO Standard” supersedes and replaces “DNV - Rules for Planning and Execution of Marine Operations”. See
also Table 1-2.
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1.1.2.2 General recommendations for planning, loads associated with and the design of marine operations are
given in DNV-OS-H101 and DNV-OS-H102.
1.1.2.3 Complementary guidance and recommendations for lifting operations in air are given in DNV-OSH205.
1.1.2.4 For positioning and station keeping of installation vessels, relevant requirements in DNV-OS-H203
should be considered.
1.1.3 Conditions for use
1.1.3.1 The objectives of this Standard are stated in DNV-OS-H101 Sec.1 A.
1.1.3.2 The general conditions for use of this Standard are stated in DNV-OS-H101 Sec.1 B200.
1.2 References
1.2.1 Numbering and cross references
1.2.1.1 Table 1-1 defines the numbering system used throughout this standard, in comparison with that
adopted in some of the DNV-H series of offshore standards, published to date. See Table 1-2.
1.2.1.2 The text in this standard includes references to the documents listed in Table 1-2. If indicated where
the references are given, the referenced text shall be considered as part of this standard.
Table 1-1 Numbering
Level
Sections
Sub-Sections
Paragraphs
Items
Numbering
1
1.1
1.1.1
1.1.1.1
Numbering in some published DNV-H standards
Sec. 1, 2, 3…
A., B., C.….
A 100, A 200, A 300…
101, 102.., 201, 202.., 301, 302…
1.2.1.3 Requirements herein are based on the document revisions listed in Table 1-2; however the latest
revision shall normally be applicable, unless otherwise agreed.
Guidance note:
The agreement should be made (normally through contracts) between the parties involved, typically Company,
Contractors and MWS.
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DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
Sec.1 Introduction – Page 9
Table 1-2 Normative references
Reference
DNV-OS-E407
DNV-OS-F101
DNV-OS-F201
DNV-OS-H101
DNV-OS-H102
DNV-OS-H201
DNV-OS-H202
DNV-OS-H203
DNV-OS-H204
DNV-OS-H205
Revision
Oct 2012
Oct 2013
Oct 2010
Oct 2011
Jan 2012
Apr 2012
See note
Feb 2012
Nov 2013
Apr 2014
Title
Underwater Deployment and Recovery Systems
Submarine Pipeline Systems
Dynamic Risers
Marine Operations, General (VMO Standard Part 1-1)
Marine Operations, Design & Fabrication (VMO Standard Part 1-2)
Load Transfer Operations (VMO Standard Part 2-1)
Sea Transport (VMO Standard Part 2-2)
Transit and Positioning of Offshore Units (VMO Standard Part 2-3)
Offshore Installation Operations (VMO Standard Part 2-4)
Lifting Operations (VMO Standard Part 2-5)
Note:
Publication of the complete DNV-OS H-series is planned during the period October 2011 - January 2015. Each OS will enter into force
on the date of publication. Until the OS is published the relevant requirements in “DNV - Rules for Planning and Execution of Marine
Operations” shall be considered governing.
1.2.1.4 The documents listed in Table 1-3 include information that through references in this text, clarify and
indicate acceptable methods of fulfilling the requirements given in this standard.
1.2.1.5 The latest revision of the informative references should normally be considered.
Table 1-3 Informative references
Reference
DNV-RP-H101
DNV-RP-H102
DNV-RP-H103
DNV-RP-C205
DNV-RP-A203
DNV-RP-J301
DNV-RP-H201
DNV 2.7-3
DNV Ship Rules
DNV-OS-E303
DNV CN30.4
ND/0029
ND/0035
IMO MSC/ Circ. 645
NORSOK U-102
IMCA AODC 032
IMCA D 014
ISO-13628-2
ISO-13628-5
ISO-13628-11
API 17E
API 17J
API 17B
Title
Risk Management in Marine- and Subsea Operations
Marine Operations during Removal of Offshore Installations
Modelling and Analysis of Marine Operations
Environmental Conditions and Environmental Loads
Qualification Procedure for New Technology
Subsea Power Cables in Shallow Water Renewable Energy Applications
Subsea Lifting (Planned issued October 2014)
DNV Standard for Certification No 2.7-3 – Portable Offshore Units
DNV Rules for Classification of Ships
Offshore Fibre Ropes
DNV Classification Note 30.4 Foundations
GL Noble Denton – Guidelines for Submarine Pipeline Installation
GL Noble Denton – Guidelines for Offshore Wind Farm Infrastructure Installation
Guidelines for vessels with dynamic positioning systems
Remotely Operated Vehicle (ROV) Services
Remotely Operated Vehicle Intervention During Diving Operations
International Code of Practice for Offshore Diving
Design and operation of subsea production systems - Part 2: Unbonded flexible pipe systems for
subsea and marine applications
Design and operation of subsea production systems - Part 5: Subsea umbilicals
Design and operation of subsea production systems - Part 11: Flexible pipe systems for subsea
and marine applications
Specification for Subsea Umbilicals, Fourth Edition (ISO 13628-5:2009, Identical Adoption)
Specification for Unbonded Flexible Pipe
Recommended Practice for Flexible Pipe
DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
Sec.1 Introduction – Page 10
1.3 Definitions
1.3.1 Verbal forms
1.3.1.1 Verbal forms of special importance are defined as indicated below in this standard.
Table 1-4 Verbal forms
Term
Shall
Should
May
Definition
Verbal form used to indicate requirements strictly to be followed in order to conform to the document.
Verbal form used to indicate that among several possibilities one is recommended as particularly suitable,
without mentioning or excluding others, or that a certain course of action is preferred but not necessarily
required.
Verbal form used to indicate a course of action permissible within the limits of the document.
1.3.2 Terminology
1.3.2.1 Terms of special importance are defined as indicated below in this standard. See also DNV-OS-H101
for general terms and DNV-OS-H205 for lifting related terms.
Table 1-5 Terms
Term
Characteristic condition:
Characteristic load:
Design load:
Design sea state:
Object:
Product:
Short term wave
condition:
Significant wave height:
Snap force:
Zero crossing wave
period:
Description
A condition which has a defined probability of being exceeded within a defined time period,
see also DNV-OS-H101 Sec.3 A300.
The reference value of a load to be used in the determination of load effects. See also DNVOS-H102, Table 3-1.
The design value of a load found by combining the relevant characteristic load(s) multiplied
by the appropriate load factor(s).
The short term wave condition which forms a basis for the design and design verification.
The structure handled during the marine operation, typically a structure, pipeline, cable, riser,
umbilical etc. that will be permanently installed subsea.
This is used as a collective term for the various objects covered in Sec.6.
A wave condition where significant wave height and zero crossing wave period are assumed
constant in the duration time, typically 3 hrs.
Four times the standard deviation of the surface elevation in a short term wave condition
(approximately equal to the average wave height associated with the highest third of all
waves).
Short-duration dynamic force associated with sudden changes in velocity of a lifted object,
or sudden tensioning of a slack cable system, e.g. in the case of uncontrolled ‘lift-off’ from
a supply vessel or sea-bed, and/or during uncontrolled deployment/recovery through the
splash-zone.
Average wave period, i.e. average time interval between upward or downward crossings of
the still water level by the water surface.
1.3.3 Abbreviations
1.3.3.1 The list below defines abbreviations used within this standard:
ADS
AHC
ALS
CoB
CoG
DAF
DAFconv
DP
FMEA
HAZOP
MBL
MPI
PHC
ROV
Atmospheric diving systems
Active heave compensating
Accidental limit state, see DNV-OS-H102
Centre of buoyancy
Centre of gravity
Dynamic amplification factor
Converted DAF, i.e. DAF calculated as a function of weight in air (m g) of the object
Dynamic positioning
Failure mode effect analysis
Hazard and operability study
Minimum breaking load
Magnetic particle inspection
Passive heave compensating
Remotely operated vehicle
DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
Sec.1 Introduction – Page 11
TLP
ULS
UT
VIV
Tension leg platform
Ultimate limit state, see DNV-OS-H102
Ultrasonic testing
Vortex induced vibration
1.3.4 Symbols
1.3.4.1 The list below defines symbols used within this standard:
AROV
dcab
Fcur
Fhyd
Fpd
Fsnap
Fstatic
Fstatic-min
Fstatic-max
Ftotal
g
Hs
K
lcab
m
TR
vcur
ηct
Projected cross sectional area of ROV.
Diameter of (submerged) cable.
Horizontal current force on ROV
Characteristic hydrodynamic load.
Forces on object when pulled down in lock-in position.
Characteristic snap load
Static submerged weight of object.
Minimum static submerged weight
Maximum static submerged weight
Total (static + hydrodynamic) characteristic load on the object
Acceleration due to gravity.
Significant wave height of design sea state.
Stiffness of hoisting system.
Projected length of submerged cable.
Mass of object in air.
Operation reference period, see DNV-RP-H101.
Maximum current velocity.
Characteristic single amplitude vertical motion of crane tip.
DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
Sec.2 General requirements – Page 12
SECTION 2 GENERAL REQUIREMENTS
2.1 Planning
2.1.1 General
2.1.1.1 Subsea operations shall be planned and documented according to the requirements and philosophies
given in DNV-OS-H101 Sec.2.
2.1.1.2 Operational requirements/restrictions, see [2.10], shall be duly considered in the planning phase.
2.1.2 Operation period
2.1.2.1 The required operation reference period TR (defined in DNV-OS-H101 Sec.4 B200) should be
thoroughly evaluated at an early stage.
2.1.2.2 The start and end points for subsea installation operations shall be Safe Conditions. The Safe
Conditions and point(s) of no return, if any, should be clearly defined. Safe Condition is defined in DNV-OSH101 Sec.2 A102 Guidance Note. See [6.2.3] for continuous operations.
Guidance note:
The time expected for the removal of seafastening should normally be included in the operation reference period. The
start of seafastening removal will normally be defined as a point of no return unless equipment and procedures for
reinstatement of seafastening has been planned and accounted for in the operation reference period.
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2.1.3 Environmental conditions
2.1.3.1 Subsea installation operations will normally be weather restricted; planning should include a thorough
evaluation of the expected environmental conditions to ensure that there will be adequate weather windows for
the planned operations.
Guidance note:
A subsea installation operation could comprise several sub-operations, each with different limiting environmental
criteria.
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2.1.3.2 All possible environmental conditions (see DNV-OS-H101 Sec.3) shall be evaluated and considered
during planning.
2.1.4 Critical design parameters
2.1.4.1 When evaluating a subsea operation, the parameters listed below should as found relevant, be taken
into account prior to establishing the operation and design criteria (see also DNV-OS-H101 Sec.4 B).
a)
b)
c)
d)
e)
f)
g)
h)
i)
j)
k)
l)
m)
n)
o)
p)
q)
water depth
tide
on bottom visibility
accuracy of survey equipment
available current data
wave/wind statistics for area in question
the expected operation reference period
expected time to reverse the operation
type of operation
contingency procedures, e.g. retrieval or abandonment of object
type of installation vessel/equipment
weather forecast and monitoring uncertainties
vessel response characteristics
deck handling/over-boarding restrictions
type of lifting gear
crane capacity and specifications
weight of crane wire (in deep water)
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r) crane tip motion
s) crane hoisting/lowering speed
t) hydrostatic and hydrodynamic effects (air filled structure or not)
u) entrapped air
v) submerged weight
w) tugger line forces
x) operational restrictions on tugger line disconnection
y) guide wire forces and winch speed limitations
z) soil conditions and soil properties
aa) seabed topography
ab) load reducing systems (heave compensation capacities)
ac) vessel DP capability /position keeping systems
ad) ROV station keeping capability
ae) ROV working range
af) complexity of ROV tasks (e.g. ROV Interfaces on structure).
2.1.5 Installation site survey
2.1.5.1 The planning process shall incorporate information gathered from site surveys to account for prevailing
soil conditions, see [2.1.4.1] item z) and aa).
2.1.5.2 In general, installation site surveys should be carried out as described in DNV-OS-H204 Sec.2 [4.3].
Guidance note:
The below listed aspects could be of relevance for subsea installations and the survey should hence give adequate
input to evaluate properly these aspects:
a) Limiting set-down velocity. I.e. to estimate soil-structure interaction effects due to installation impact loads.
b) Suction forces (reverse end bearing) during rapid pull-out.
c) Off-target position of object, both due to alternative permanent positions and due to contingency set-down.
d) Scour/build-up caused by current.
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2.1.6 Route survey
2.1.6.1 For pipelines, umbilicals, flexibles, cables and submerged tows, route surveys shall be carried out
along the total length of the planned route to provide sufficient data for design and installation related activities.
Guidance note:
More information regarding route surveys and their purpose can be found in the following documents/sections:
— For pipelines: DNV-OS-F101 Sec.3.
— For subsea cables: DNV-RP-J301 [3.4]
— Submerged pipeline towing: DNV-OS-F101 Sec.10 F500
— Bundles: [4.3.3.3]
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2.1.7 Risk management
2.1.7.1 Operational risk should be evaluated and handled in a systematic way see DNV-OS-H101 Sec.2 C.
2.2 Documentation
2.2.1 General
2.2.1.1 General requirements for documentation are given in DNV-OS-H101 Sec.2 B.
2.2.2 Design documentation
2.2.2.1 Depending on type of structure the following design documentation is normally required as a minimum:
— Design load evaluations/calculations/analysis including motion response characteristics for installation
vessel(s).
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—
—
—
—
—
Structural strength analysis and stability calculations for the object.
Strength and capacity calculations for all equipment and (temporary) structures.
Technical specifications, certificates and test reports for equipment.
Documentation of soil characteristics.
Vessel data, stability and strength verifications.
Guidance note:
For lifting appliances the design documentation should normally be given in the form of certificates - however, see
also [2.3.2].
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2.2.2.2 If monitoring is used as a means of operational control, expected target monitoring results should be
documented by calculation. Target monitoring values and acceptable tolerances on them should be clearly
defined.
2.2.3 Operation manual
2.2.3.1 An operation manual shall be prepared, see DNV-OS-H101 4 G200.
2.2.3.2 The items listed below should be adequately covered in the manual. A clear reference to the documents
where this information could be found may normally be considered as adequately covered.
a) Operational organisation chart(s) and responsibilities of key personnel.
b) Description of limiting operational environmental criteria and requirements for weather forecasting and
wind/wave/current monitoring.
c) Detailed operation schedule and weather window requirements, ref. DNV-OS-H101 Sec.4 B.
d) Pre-launch/deployment checklists ensuring that all required preparations have been carried out.
e) Clearly defined and measurable installation tolerances.
f) Target position of the object and vessels during all phases of the operation.
g) Procedures for handling of possible contingency situations (see [2.10.6]).
h) Object limiting structural criteria (e.g. max allowable tension, min. allow. tension, MBR, etc.)
i) Description of equipment limitations.
j) Detailed description of operational steps, supported by relevant drawings and sketches.
2.3 Lifting appliances
2.3.1 Crane
2.3.1.1 Crane and crane vessel shall comply with the requirements in DNV-OS-H205 [2.2].
2.3.2 Other lifting appliances
2.3.2.1 The capacity and quality of underwater deployment and recovery systems should generally be
documented as adequate according to the principles described in DNV-OS-E407.
2.3.2.2 If a winch is chosen for deployment of structures to the seabed, the winch shall be regarded as a lifting
appliance.
Guidance note:
Documented capacity and load-testing as for a crane, see e.g. DNV 2.22, of deployment winches are mandatory. Other
requirements to cranes e.g. to monitoring and alarm systems can be evaluated on a case by case basis.
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2.3.2.3 Structures, such as A-frames, forming part of a lifting appliance intended for subsea lifts should
normally fulfil the design, fabrication and test requirements applicable to cranes; see DNV-OS-H205 [2.2].
Guidance note:
Alternatively, it can be acceptable to define these parts as structures, see DNV-OS-H205 Sec.5. Normally this
approach would apply to temporary lifting appliances, used for specific operation(s). Note also Table 5-1 in
DNV-OS-H205.
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2.3.2.4 If traction winches are used for deep water installations, due considerations shall be made to the
possible failure modes of the rope.
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Guidance note:
System performance will depend on the type of rope and winch design. Discard criteria for the rope should be
established based on relevant failure modes identified. See DNV-OS-E303 Offshore fibre ropes (Condition
Management Program).
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2.4 Load and motion limiting systems
2.4.1 General
2.4.1.1 Load and motion limiting systems are devices used to minimise relative motions and dynamic loads
experienced by a lifted object, during subsea lifting operations.
Guidance note:
Load and motion limiting systems can consist of active or passive heave compensation systems, shock absorbers, soft
springs and fenders. Heave compensating systems are generally described DNV-RP-H201 App.C.
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2.4.1.2 Load and motion limiting systems shall be designed, fabricated, installed and tested in accordance with
relevant recognised codes and standards, see DNV-OS-H101 Sec.1 B305.
2.4.1.3 Adequate capacity and functionality for the intended use shall be documented. A thorough description
of the system and its use during the planned lifting operation shall be provided.
Guidance note:
Typical elements to be evaluated are structural capacity, hydraulic capacity, sufficient stroke length, power supply,
adequate cooling etc.
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2.4.1.4 Unless adequate reliability can be documented, contingency cases considering malfunction of the load
/ motion limiting system shall be investigated. Calculations may be carried out assuming accidental limit state
(ALS).
Guidance note:
Adequate reliability implies a documented risk of catastrophic failure less than 1/10,000 per operation. Hence, if the
risk of malfunction is greater than 1/10.000 the possible consequence of malfunction, which could be “catastrophic
failure”, should be analysed. All possible failure modes of load limiting systems should be identified using applicable
risk identification techniques and methods as described in DNV-OS-H101 Sec.2 C200. It should be documented that
the installation can be safely completed or abandoned at all times, without jeopardizing the integrity of the object.
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2.4.2 Active heave compensation systems
2.4.2.1 A subsea lifting operation that relies on an active heave compensation (AHC) system shall be carefully
designed, ensuring that the operation is carried out in accordance with the system’s operational limitations and
operating procedures.
Guidance note:
Consideration of an accidental case (as described in [2.4.1.4]) will normally be required. As a base case therefore, it
is recommended to calculate hydrodynamic loads without considering AHC systems.
For sub-operations mentioned in [2.4.2.3] it is normally acceptable to take into account the motion (and if applicable
load) reducing effect of an AHC system. The AHC function should be checked before the sub-operation and
contingency procedures in case of an unsuccessful check should be established in order to fulfil the requirement in
[2.4.1.4].
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2.4.2.2 Efficiency of the heave compensator (in terms of stroke length and /or max pay out/in speed) shall
generally not be taken higher than 80% of the theoretical operational values.
Guidance note 1:
A safety factor of 0.9 on the stated and documented efficiency reduction factor is recommended, i.e. if the heave comp
system has 90% stated / documented efficiency, the maximum efficiency factor should be 0.9 ⋅ 0.9 ≈ 0.8, or 80%.
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Guidance note 2:
The test results and operational records used to derive the efficiency factor should be based on data from operations
where the environmental conditions, depth, weight of object and other effects influencing the performance of the
heave compensation system are comparable with those of the planned operation.
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2.4.2.3 The motion (and if applicable, load) reducing effect of an AHC system should normally be applied
during sub-operations of limited duration only, e.g. final landing, final positioning or initial phase of retrieval
of a subsea object.
Guidance note:
Acceptable duration of AHC operations should be evaluated based on the criticality of the operation and the reliability
record of the AHC.
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2.4.2.4 Characteristics and performance of AHC systems shall be documented (see [2.4.1.3]). Performance
may be documented by testing and relevant operational records.
Guidance note:
Guidelines for performance of AHC systems are presented in DNV-RP-H201 App.C.
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2.4.2.5 If there is a high risk of significant suction forces and/or soil friction, the appropriate crane mode and
its limitations should be duly considered as indicated below:
— AHC mode shall only be used in combination with measures to avoid excessive loads.
Guidance note:
Lifting off in AHC mode can give the crane operator control of the lifting speed. There is however a risk of excessive
loading.
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— Tension Control mode shall be used only in combination with measures to avoid excessive speed.
Guidance note:
Whilst lifting off in Tension Control mode can provide the crane operator with tension control, there is a risk of
excessive lifting speeds.
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2.4.3 Passive heave compensation systems
2.4.3.1 The effect of passive heave compensation (PHC) systems (e.g. spring/damper devices) may be
accounted for in hydrodynamic load calculations.
Guidance note:
The dynamics of PHC systems can be calculated following the guidelines in DNV-RP-H103 Sec.5. The effect of such
systems may also be implemented as soft springs in snap load calculations (see DNV-RP-H103 [4.7]).
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2.4.3.2 The characteristics and performance of the PHC system shall be documented (see [2.4.1.3]). The
performance of the system can be documented by testing and/or operational records.
Guidance note 1:
Guidelines for performance of PHC systems are presented in DNV-RP-H201 App.C
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Guidance note 2:
PHC systems can be set up in different ways e.g. with full stroke available to resist loads above the threshold setting
or with the stroke divided so that both load increases and reductions can be absorbed (within the available part-stroke
lengths).
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Guidance note 3:
If the rigging includes multiple PHC systems the stability of the system should be demonstrated.
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2.4.3.3 If relevant, efficiency of the heave compensator in terms of stroke length and /or max pay out/in speed
should generally not be taken higher than 80% of the theoretical operating range.
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Sec.2 General requirements – Page 17
Guidance note:
To use an efficiency factor of 80%, system performance of 90% of theoretical values should be documented.
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2.5 Lifting equipment
2.5.1 General
2.5.1.1 See DNV-OS-H205 Sec.4 for general definitions and requirements.
Guidance note:
This sub-section includes clarifications and additional recommendations regarding use of lifting equipment for subsea
operations.
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2.5.1.2 Subsea lifting equipment materials must be carefully selected to take account of the potential failure
mechanisms that may be caused or accelerated by the environment such as galvanic corrosion, stress corrosion
cracking or the effects of cathodic protection systems.
2.5.2 Design considerations
2.5.2.1 Lifting equipment shall be verified for the worst combination of dynamic hook load and all reasonably
foreseeable load effects (including unintentional ones).
2.5.2.2 Lift points should be configured such that the risk of damage and/or accidental release of slings (due
to possible impact loads) are negligible.
2.5.2.3 Lift point layout and rigging design shall ensure adequate stability and acceptable tilt of the object
during all phases.
Guidance note 1:
If adequate lift stability is not obvious by inspection, the risk of overturning should be evaluated, documented and
mitigated. Adequate stability of the object should be ensured considering:
— all possible unfavourable combinations of sling loads, buoyancy, CoB and CoG (CB and CG), see also DNV-RPH103 [3.6] and [5.6.1.6]
— vertical wave loads
— horizontal (differential) wave loads
— current loads
— lift dynamics.
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Guidance note 2:
Due to buoyancy, the tilt of the lifted object can change when being submerged. This should be considered when
defining the optimal tilt in air and water.
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2.5.2.4 Lifting equipment should be designed with attention given to the planned subsea release/connection of
the rigging.
2.5.2.5 Lift points and exposed areas of the lifted object should be designed to allow slackening of lifting wires
and release and controlled recovery of rigging items without snagging.
2.5.2.6 All lifting equipment shall as a minimum incorporate one safety barrier / retention mechanism (safety
latch, split-pin/cotter-pin etc.), itself being adequately secured and protected against accidental release.
Guidance note:
These safety barriers / mechanisms should not be affected by lifting or external loads.
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2.5.2.7 For lifting operations with dynamic forces that are large relative to the static weight of the object, it is
considered normal practise to incorporate a minimum of two safety barriers, again suitably protected against
accidental release. The primary safety barrier should have adequate strength to accommodate any possible load
direction.
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Guidance note:
ROV spring safety latch hooks should be avoided if there is any possibility of slack slings/snap forces. This because
even if the latch has a secondary release barrier the hook may come out of position and the latch take the load which
it is not dimensioned for.
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2.5.2.8 Lifting equipment containing hydraulic, pneumatic or other remotely operated release mechanisms,
shall be designed to fail safe.
2.5.2.9 Structural lifting elements, like spreader bars, lifting frames, etc. should preferably be free flooding. If
not, free flooding maximum depth rating to be calculated and marked on the equipment, see [3.3.2.1].
2.5.2.10 If trunnion-type lift points are used, slings should be mechanically secured against significant
displacement and unintended release during phases of variable sling load.
2.5.2.11 The lifting arrangement should have sufficient length to allow crane hook to be connected at deck
level in order to avoid working at height on board the installation vessel/barge.
Guidance note:
If not possible e.g. due to lifting height a proper plan for the hooking on including if required physical means as
rigging platforms, etc. needs to be in place.
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2.5.3 Wet-storage of lifting equipment
2.5.3.1 Lifting and other temporary equipment stored on the seabed shall have adequate resistance against all
possible mechanisms of degradation - material properties shall be justified and documented accordingly.
2.5.3.2 If storage periods beyond normal inspection intervals are anticipated, the means for satisfying any
formal and regular inspection requirements should be agreed.
2.5.3.3 The destructive effect of cyclic loading shall be considered for equipment subject to such loading
during wet-storage (e.g. pick-up lines connected to buoys).
2.5.4 Custom-made lifting equipment
2.5.4.1 Lifting equipment designed for case-specific usage shall comply with requirements in DNV-OS-H205
[5.1.5].
2.5.5 Lifting tools
2.5.5.1 Lifting tools shall comply with requirements in DNV-OS-H205 [4.3.3].
Guidance note:
A lifting tool in this sub-section is defined as a hydraulic tool, internally or externally connected to a tubular
receptacle.
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2.5.5.2 It shall be documented that the tool cannot accidentally release due to varying loads (typically low
tension) in the lift system.
2.5.5.3 Lifting tools designed for remote subsea release shall have a back-up release mechanism.
2.5.6 Test lift
2.5.6.1 The need to perform test lifts shall be considered.
Guidance note:
An onshore test-lift is recommended. The actual rigging configuration and lifted load should be used to confirm that
sling lengths and tilt are within specified tolerances and that slings / loose gear can be hooked-up and laid down, safely
and without damage.
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2.5.6.2 If the required tolerance on tilt of a submerged object is small (e.g. due to the need to engage with guide
posts), a subsea test-lift should also be considered.
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Guidance note:
The main purpose of this test is to find the tilt of the object in submerged condition. See also [2.5.2.3] GN 2. The
evaluation of need for testing should consider possible corrective action based on test results and the level of
confidence in CoG/CoB positions.
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2.6 Guiding and positioning systems
2.6.1 General
2.6.1.1 General requirements for guiding and positioning systems are given in DNV-OS-H101 Sec.6 C.
Requirements for the operational control of lifts in-air can be found in DNV-OS-H205 [2.3.2]. This section
clarifies some of the requirements in these documents and where appropriate should be considered to
supplement their requirements.
2.6.2 Control of lift
2.6.2.1 Adequate control of any lift shall be ensured during all phases. See DNV-OS-H205 [2.3.2] for
requirements relating to the lifting in-air phase.
2.6.2.2 In cases where the retrieval of a lifted object to deck is necessary, the following should be considered:
— anticipated weight increase and instability due to the effects of entrapped water, debris and drainage during
lifting
— available deck space
— guides and bumpers
— tugger wire system
— reinstatement of seafastening.
Guidance note:
The above is also applicable for retrieval/backloading of heavy rigging, spreaderbars, installation tools etc.
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2.6.2.3 Subsea disconnection of tugger lines should be suitably planned. If ROV’s are to be used for
disconnecting tugger lines, consideration should be given to the limitations and recommendations in [2.9.1].
2.6.3 Guide lines/guide wires
2.6.3.1 Guide wires should be used to prevent rotation of the lifted object during installation. It will normally
be sufficient to prevent rotation during only the final stages of lowering. Other means of preventing rotation
can be acceptable.
2.6.3.2 If guide/pull-down lines fixed to a pre-installed subsea template or similar require a fixed vessel
heading, the weather criteria specified for the operation should reflect this.
2.6.3.3 Guide wire tension shall be adjusted to suit the weight of the installed object and possible current forces
on the object/lifting gear.
2.6.3.4 If guide wire winches are used to provide wire tension, the weight of the guide wire shall be accounted
for when defining the required winch tension/capacity.
2.6.3.5 Guide wire winch speed shall be considered when defining the operational limiting criteria for the
operation.
2.6.3.6 Capacity of guide-wire attachment points on subsea structures shall satisfy the structural strength
requirements given in DNV-OS-H102.
2.6.3.7 The guide-wire system shall include a weak link. The capacity of the weak link shall not exceed the
design load of the guide-wire attachment, or 80% of the system MBL, whichever is less.
2.6.4 Bumpers and guides
2.6.4.1 If a guide system on a subsea structure incorporates more than one guidepost, the use of guide posts of
differing length should be considered to facilitate landing of the object.
2.6.4.2 If a guide system consists of guide funnels or similar, the connection of the guide receptacle to the
structure should be designed with consideration given to installation loads (e.g. overload / impact) that could
damage the integrity of primary structural elements of the object.
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2.6.4.3 The design of guiding systems should consider contingency cases and should not limit retrieval of the
object.
2.6.4.4 Due consideration shall be paid to the possibility of the object/structure becoming jammed in the guide
system.
Guidance note:
Primary and a secondary guiding systems can be required to install structures with smaller tolerances than can be
safely achieved (e.g. without risk of jamming) by one system alone. Two independent guiding systems can also be
required in cases where large motions are expected. The primary system should be designed according [2.6.4.1] and
[2.6.4.2]; the secondary guiding system being designed to resist residual forces and achieve final alignment/
installation.
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2.6.4.5 Design requirements for bumpers and guides are given in [3.4.3].
2.7 Installation aids
2.7.1 General
2.7.1.1 General requirements for system and equipment design are given in DNV-OS-H101 Sec.6 A.
Guidance note:
Installation aids are defined herein as purpose-built equipment, used to assist and control a specific phase of a lifting
operation, in turn making it safer and more efficient.
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2.7.2 Design considerations
2.7.2.1 Installation aids should be located such that they are not damaged during preceding operations, e.g.
lifting of structures, handling of piles, opening/closing of hatches, etc.
2.7.2.2 Temporary attachments having the potential to damage the structure or other equipment should be
removed after final use without undue delay.
2.7.2.3 The use of surface-supplied gas/hydraulic power to connect/lock the object to a pre-installed seabed
unit should be avoided. If used, the risk of sustaining of mechanical damage during lowering/positioning
should be assessed and minimised; a sufficient back up system can be necessary to mitigate undue risk.
2.7.2.4 Subsea sheaves, blocks and other equipment that require lubrication during operation should have
closed or pressure-compensated lubrication systems.
2.7.3 Design factor
2.7.3.1 Rigging equipment used for purposes other than lifting should be used with safety factors adequate for
the intended use.
Guidance note:
If the consequence of failure is considered tolerable by all involved parties, a reduced consequence (safety) factor can
be acceptable. E.g. if the rigging is used for pulling/hold-back only and the consequences of rigging failure are
regarded as negligible, a lower consequence factor may be applied, see DNV-OS-H205 [4.1.5].
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2.8 Miscellaneous systems
2.8.1 Dynamic positioning systems
2.8.1.1 General requirements for the operation of DP (Dynamic Positioning) vessels are given in DNV-OSH203 Sec.5.
2.8.1.2 DP operations requiring DP equipment class 2 and 3 shall be restricted (planned, see also [2.8.1.3] and
[2.8.1.4] below) based on the power/thrust available after worst single failure.
Guidance note:
The worst single failure concept is further described in DNV Ship Rules Pt.6 Ch.7- Dynamic Positioning Systems, and
in IMO MSC/Circ. 645.
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2.8.1.3 DP capability should be continuously monitored throughout the operation, and the operation should be
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Sec.2 General requirements – Page 21
safely terminated if the DP-vessel will no longer be able to keep position if the single failure criterion
applicable to the equipment class should occur. In this context deterioration of environmental conditions and
the necessary time to safely terminate the operation should also be taken into consideration. Possible increase
in current forces and uncertainty in the weather forecasting (see DNV-OS-H101) shall be accounted for.
Guidance note:
DP capability plots should be used to verify power/thrust availability based on expected environmental conditions.
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2.8.1.4 Should a stand-off mode be impossible, preparations for abandoning or retrieval of an object should be
made in due time, prior to reaching the consequence analysis alarm.
Guidance note:
Stand-off mode is defined as a situation where operation is discontinued and vessel/product/object is temporarily held
in a safe condition. The Stand-off mode shall be designed as a safe condition as defined in DNV-OS-H101 Sec.2
A102. Adequate planning should be made to accommodate any vessel heading limitations and object handling
restrictions.
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2.8.1.5 Minimum clearances between a DP vessel and any fixed or floating structures shall be defined
considering the minimum clearances indicated in DNV-OS-H203 Sec.5 C200, see also DNV-OS-H205
[2.3.3.5].
2.8.1.6 For complex and/or close proximity DP operations involving one or more DP vessels, a DP operation
procedure shall be presented.
Guidance note:
The DP procedure shall as a minimum include:
— a description of the work that is planned performed
— weather criteria (force and direction)
— minimum distances between vessels
— pre-operation DP testing requirements
— foot print testing should be included if found relevant based on the required station keeping accuracy
— reference systems setup, including evaluation of possible shadow effects on aerials and thrust interference on
hydro-acoustic transducers
— engine room and switchboards configuration
— communication procedures, internally and between vessels
— copy of HAZOP/risk analysis findings and risk reducing measures
— training/competence level of key DP personnel.
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2.8.2 Ballasting systems
2.8.2.1 For operations requiring ballasting of an object, a suitable ballast control and monitoring system should
be provided.
2.8.2.2 Ballast systems utilising external umbilical power supply are subject to the same recommendations as
in [2.7.2.3]. The ballast system should be designed to fail safe in case of umbilical damage.
2.8.2.3 All ROV operated valves should be clearly marked according to function and with open/shut (O/S)
positions. Valve indicators on critical valves can be considered necessary for visual verification purposes.
2.8.2.4 Analogue pressure gauges to be monitored by ROV shall be of adequate size and have easy-to-read
indication and figures.
2.8.2.5 Special back-up or monitoring equipment can be required to avoid uncontrolled ballasting and overpressurisation.
2.8.3 Atmospheric diving systems
2.8.3.1 Atmospheric diving systems (ADS) shall be certified in accordance with recognised standards.
2.8.3.2 The system and operational procedures should be adequate for the intended work scope. IMCA D 014
can be consulted for detailed advice and recommendations.
2.8.3.3 ADS should in general incorporate adequate back-up, enabling 24 hours (around the clock) operability
if required.
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Sec.2 General requirements – Page 22
2.8.3.4 Operational reliability should be documented through presentation of dive logs, maintenance records
etc.
2.8.3.5 It should be documented that the ADS system is capable of operating under the given design and
operational criteria.
2.9 ROV operations
2.9.1 Planning
2.9.1.1 ROV systems and tooling should be selected based on the environmental conditions expected at the
worksite during the planned and contingency intervention/observation tasks.
2.9.1.2 When planning for a subsea operation, the following ROV limitations and recommendations should be
noted:
a) Minimum practical operational depth in the expected wave conditions, also considering possible wake from
vessel thrusters.
b) ROV working range, i.e. maximum horizontal offset vs. available tether length, considering the worst
expected current conditions.
c) Planning and design of the ROV operation shall as far as possible minimise the operational influence of the
ROV operator's skill and experience.
d) Poor visibility due to e.g. disturbed soil conditions, stirred up by contact or thruster use close to seabed.
e) Access to working site.
2.9.1.3 The station keeping capability and manoeuvrability of the ROV during operation shall be considered.
If the ROV is carrying equipment or is equipped with tooling packages/skids, this needs to be accounted for.
Guidance note:
ROV operations involving moving targets should not normally be undertaken and any ROV manipulator or tooling
operation that requires the pilot to actively control the position of the ROV during performance of the task should be
avoided.
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2.9.1.4 All essential ROV interfaces should have appropriate grab bars or other means for stabilizing ROV.
2.9.2 Schedule and contingency
2.9.2.1 ROV downtime, both planned and possible/unforeseen (see DNV-OS-H101 Sec.4 B300 and B400),
should be taken into consideration when establishing the required weather window.
Guidance note:
ROV contingency procedure(s) developed to ensure that one ROV down failure will not (significantly) compromise
the time to safe position may be considered. See also [2.9.2.3].
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2.9.2.2 Realistic ROV recovery time, both for planned maintenance and repairs shall be taken into account
during planning of the operation.
2.9.2.3 Subsea operations, where operation reference period is based on there being at least one operational
ROV at all times, should be equipped with at least two independent ROV spreads. The need for backup of
essential ROV tools should be assessed and if applicable the time needed to switch ROV tools/skids between
ROVs should be accounted for in the planning.
2.9.2.4 The ROV crew should be sufficient to provide 24 hours (around the clock) operability.
Guidance note:
Time/schedule critical ROV operations always implies 24hrs coverage, but such coverage may be deemed not
necessary on some ROVs and OBSROVs.
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2.9.3 Maintenance and tests
2.9.3.1 Prior to acceptance of ROV operations, maintenance records and dive logs for each ROV should be
presented. Sufficient spares should be available.
2.9.3.2 For complex and critical stages of the installation that are dependent on ROV operations, Client/
Contractor shall demonstrate ROV capability of executing the planned intervention. This may be demonstrated
by used of 3D models, mock-up tests, previous experience, etc.
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Sec.2 General requirements – Page 23
2.9.3.3 Function testing of ROV, ROV equipment and survey spread should be part of the test program
described in [2.10.4.1].
2.9.4 ROV Tools
2.9.4.1 All tools shall be adequate for the intended work task.
2.9.4.2 Tools shall be adequately tested and calibrated. Cutting tools shall be tested on deck (using similar wire
type) prior to operation.
2.9.4.3 Tools can influence the ROV operability and power consumption. This should be duly considered in
the ROV/tool selection process.
2.9.5 Operation
2.9.5.1 If complex operations reliant on the skill of the ROV operator alone cannot be avoided, ROV operator
experience shall be evaluated - training sessions specially adapted for the proposed operation can be
appropriate.
Guidance note:
See also [2.9.1.2]c, [2.9.3.2] and [2.10.5.2].
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2.9.5.2 ROV thruster capacity for time critical operations should be at least 30% higher than the maximum
expected current force acting on the ROV and its umbilical.
Guidance note:
The horizontal current force on the ROV and the submerged cable may be taken as:
Fcur = 0.615(dcab ⋅ lcab + AROV) vcur 2[kN]
where
dcab:
lcab:
AROV:
vcur:
diameter of submerged cable [m]
projected length of submerged cable [m]
projected cross sectional area of ROV [m2]
maximum current velocity [m/s]
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2.9.5.3 For operations using both ROV(s) and diver(s), any restrictions on simultaneous working should be
clarified and considered in advance.
Guidance note:
For guidance on safety considerations that should be taken into account when divers are working with or in the vicinity
of ROVs, see AODC 032 ‘Remotely Operated Vehicle Intervention during Diving Operations’. These considerations
include entanglement of umbilicals, physical contact and electrical hazards.
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2.9.5.4 Wire cutting by use of ROVs should only be performed on slack wire ropes or on ropes with very low
tension, e.g. carrying own weight only.
2.9.6 Navigation
2.9.6.1 Means for locating and tracking of the ROV from the surface are required for navigational purposes
and emergency recovery.
Guidance note:
There is a potential risk of acoustic interference, such as shadowing or noise under several conditions, for example if
several vessels are operating in the same area. Frequencies for acoustic beacons should be selected to avoid
interference.
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2.9.7 Launching restrictions
2.9.7.1 ROV launching and recovery restrictions shall be defined based on the capacity of the launch and
recovery system, including capacity of the umbilical. In addition any restrictions related to operational aspects
need to be considered.
2.9.7.2 The over-boarding system shall be safely operated within its intended design limit and due
consideration of ROV recovery needs to accounted for in the definition of the weather criteria.
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Sec.2 General requirements – Page 24
Guidance note:
— The launch and recovery system should incorporate a guide/cursor system to ensure controlled clearance with
vessel side during lowering through the splash zone.
— Overboard launching and retrieval of large ROV's should not take place in sea states exceeding 2.5-3.0 m (Hs) if
not the ability to operate in a safe manner under more severe conditions has been documented.
— Moon-pool ROV operations may be extended to Hs < 5-6 m, depending on the motion characteristics of the vessel.
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2.9.7.3 Launch and recovery shall as much as practically possible take place at safe distance from sensitive
subsea infrastructure.
2.9.8 Monitoring
2.9.8.1 Video monitoring of all Subsea operations should in general be provided, e.g. ROV, diver-operated,
etc. Any critical part of the operation should be performed with such monitoring.
2.9.8.2 All diving and complex Work-ROV operations should be monitored by independent ROV with
monitoring as its only task.
2.9.8.3 The ROV used for monitoring subsea operations should, as far as practically possible, be operated from
the installation vessel.
2.9.8.4 If the ROV operation has to be performed by a vessel other than the installation vessel, the stability and
reliability of the video-link system between the vessels shall be proven under the given conditions.
Guidance note:
Some operations can require a large horizontal distance between the installation vessel and the observation ROV, thus
necessitating a separate ROV vessel. The video-link should be tested prior to start of operation.
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2.9.9 Deep water ROV operations
2.9.9.1 ROV equipment capacities shall be chosen to suit the relevant depth.
Guidance note:
Both the ROV and any ROV tooling should be “depth rated”, and their stated depth limitation should not be exceeded.
General wear on the complete ROV spread during deep water operations is more extensive than during moderate
depth operations, it is important therefore that all required maintenance is done prior to operation. During deep water
operations special attention shall be given to lubrication systems which can be affected by the external water pressure.
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2.9.9.2 Current forces acting on the umbilical and ROV shall be defined, see [2.9.5.2].
2.9.9.3 Potential effects due to resonance in wires, cables, umbilicals, etc. shall be investigated and accounted
for in the design.
2.10 Operational requirements
2.10.1 Application
2.10.1.1 Requirements in DNV-OS-H101 Sec.4 will generally apply. This section should be considered
supplementary to the requirements for subsea operations.
2.10.1.2 For lifting operations in air the requirements to operational aspects given in DNV-OS-H205 [2.3] are
applicable.
2.10.2 Operation criteria
2.10.2.1 Operational limiting criteria and required weather windows shall be clearly defined for all parts of
subsea operations.
Guidance note:
Subsea operations are often comprised of several sub-operations each with different operational limitations, or can
involve a continuous interruptible operation that can be paused due to deteriorating weather conditions. Due attention
should be paid to the definition of limiting criteria forecast for such operations.
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2.10.2.2 Effects of unexpected environmental conditions such as swell and current could be critical - the
forecast and/or monitoring shall include all relevant parameters.
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Sec.2 General requirements – Page 25
2.10.3 Pre-installation surveys
2.10.3.1 A pre-installation survey of the work-site or pipeline route can be required in addition to the
installation site survey or route survey required for design purposes (covered by [2.1.5] and [2.1.6]) if:
—
—
—
—
—
time elapsed since the design base-survey is significant
a change in seabed conditions is considered likely
the installation site/route is located in areas with heavy marine activity
new installations or facilities are present in the area
seabed preparation work is performed on the installation site/within the route corridor after previous
survey.
2.10.3.2 The pre-installation survey, if required, shall determine/confirm:
— potential new hazards
— location of wrecks, submarine installations and other obstructions such as mines, debris, rocks and boulders
that might interfere with, or impose restrictions on, the installation operations
— the size as well as the location of the seabed objects and infrastructure
— that the present seabed conditions confirm those of the survey required in [2.1.5] and [2.1.6]
— previously unidentified hazards related to the nature of the installation operations.
2.10.3.3 The extent of, and the requirements for, the pre-installation installation site survey/route survey shall
be specified.
2.10.4 Testing
2.10.4.1 Applicable integration testing should be carried out. Equipment subject to such testing shall be clearly
identified in the test program, see DNV-OS-H101 Sec.4 F200.
2.10.4.2 If required system integration testing should be carried out onshore, proving that integration of all
components and tooling can be achieved. This can involve the manufacture / mock-up of simulation models.
If mock-ups are used, great care shall be taken to ensure that they replicate the actual item.
2.10.5 Organization
2.10.5.1 General requirements for the organisation, personnel qualifications and communication during
offshore installation operations are given in DNV-OS-H101 Sec.4 E.
2.10.5.2 The feasibility of subsea operations often relies on the correct completion of tasks by ROV - it should
therefore be ensured that ROV operators have the necessary experience and skills.
Guidance note:
Recommendations for manning level and ROV crew qualifications are given in NORSOK U-102, Section 6.
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2.10.6 Safety and contingency
2.10.6.1 Operations shall be carried out with due attention to safety, to minimize the risk of emergency and
contingency situations.
2.10.6.2 Detailed procedures for critical operational steps should be established, to define environmental limits
for possible contingency operations necessary to bring the object to a safe condition e.g. by abandoning or
reversing the operation, see also DNV-OS-H101 Sec.2 A400.
Guidance note:
Special considerations for contingency planning under various types of operation are provided in relevant sections.
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2.10.6.3 For lifting/handling objects over the side of a vessel, risks relating to dropped objects should be
considered, see DNV-OS-H102 Sec.3 F300.
Guidance note:
For lifting operations taking place over a vessel side it is normally recommended to establish a safe over boarding
distance from any subsea assets following the principles in DNV-OS-H102 Sec.3 F303.
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Sec.3 Loads and structural design – Page 26
SECTION 3 LOADS AND STRUCTURAL DESIGN
3.1 Loads
3.1.1 General
3.1.1.1 A thorough evaluation shall be made to identify the nature of and derive the magnitude of all possible/
relevant load effects, their appropriate characteristic value/s and combinations.
Guidance note:
Loads applicable for the type of subsea operation proposed (as indicated in [3.3]) should at least be considered. Loads
are also described for various types of operations in Sec.4, Sec.5 and Sec.6.
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3.1.1.2 Loads associated with lifting in air (described in DNV-OS-H205 Sec.3) will normally be applicable
also for subsea lifting operations.
3.1.1.3 All loads should be assessed and categorized as indicated in DNV-OS-H102 Sec.3.
3.1.1.4 Vessel motions will normally have a significant effect on loads experienced during offshore operations
and should be assessed accordingly. See [3.2].
3.1.2 Loadcases and analysis
3.1.2.1 Load analyses should be carried out as described in DNV-OS-H102 Sec.4 A.
3.1.2.2 DNV-OS-H102 Sec.4 C describes how to combine individual loads into appropriate load cases/
combinations.
3.1.2.3 Requirements for loadcases and analysis of forces for lifting in air (described in DNV-OS-H205 [3.4])
will normally be applicable to subsea lifting operations, in addition to the recommendations herein.
3.1.2.4 Further requirements for different types of subsea operations are given in Sec.4, Sec.5 and Sec.6.
Guidance note:
Recommendations for modelling and analysis of various types of marine operations are also given in DNV-RP-H103.
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3.2 Vessel motions and accelerations
3.2.1 General
3.2.1.1 General requirements for motion analysis are given in DNV-OS-H102 Sec.4 B.
3.2.1.2 The characteristic motions, velocities and accelerations of relevant reference points (e.g. crane tip) on
the installation vessel should be calculated for the defined environmental design conditions.
Guidance note:
Calculations may be done either by a refined analysis, or by acceptable documented simplified calculations, see DNVRP-H103 for guidance.
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3.2.1.3 Moderate and low sea states in open sea areas are often composed of both wind wave systems and
swell. All relevant combinations of wind seas and swell should be considered, ref. DNV-OS-H101 Sec.3 C100.
Guidance note 1:
The wave conditions in a sea state can be divided into two classes, i.e. wind seas and swell. Wind seas are generated
by local wind, while swell is not. Swell seas are waves that have travelled out of the areas where they were generated.
Note that several swell components can be present at any given location.
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Guidance note 2:
For subsea lifting operations it is normally sufficient to consider the most unfavourable relevant combination(s) of
simultaneous wind seas and swell. As a minimum the combination of wind seas and swell acting with 90° (or 270°)
difference in propagation direction should be considered. The combination of head (or stern) wind seas and swell with
propagation direction towards the crane side of the vessel/object deployment side of vessel will normally be more
severe than swell propagating in the opposite direction.
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Sec.3 Loads and structural design – Page 27
3.2.2 Characteristic vessel motions generated by wind seas
3.2.2.1 For subsea (lift) operations dependent on a fixed vessel heading, vessel responses for all wave
directions should be analysed. Spacing between the wave headings analysed should not exceed 22.5°.
Guidance note:
Analysis for 45 degrees spacing may be acceptable supported by interpolation calculations for intermediate headings.
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3.2.2.2 For subsea (lift) operations that are to be performed independent of vessel heading, vessel response
should be analysed for wave directions at least ± 15° off the vessel heading stated in the procedure.
3.2.2.3 Short crested sea with spreading n = 2 used in the directional function, ref. DNV-OS-H101 Sec.3 C902,
should be applied for operations that are independent of vessel heading.
Guidance note:
DNV-RP-H103 indicates that, for some cases, it can be acceptable to perform calculations for long-crested seas only.
If long-crested sea is used for simplicity, the following applies:
Vessel response should be analysed for wave directions at least ±20° outside the vessel heading range. The heading
range should normally be taken as a minimum of ±15°, but in some cases ±10° can be acceptable. Hence, in the latter
case the analysis should be carried out with vessel target heading ±30°.
Note that if neither other headings nor swell (see [3.2.2.1] and [3.2.3.1]) is considered, the operational limiting swell
(from other directions than the wind generated sea) should be set to “zero” (i.e. negligible).
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3.2.3 Characteristic vessel motions generated by swell
3.2.3.1 Critical swell periods should be identified and considered in the design verification, see DNV-OSH101 Sec.3 C1000.
Guidance note:
For vessel lifting operations, the following swell periods can be critical:
— Swell periods coinciding with vessel roll and pitch natural period.
— Swell period coinciding with natural period (eigenperiod) for horizontal motion (pendulum motion) of the lifted
object in air, given by DNV-RP-H103 [9.2.1.6].
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3.3 Loads
3.3.1 Weight and buoyancy
3.3.1.1 The object weight, CoG, buoyancy and CoB should be defined according to DNV-OS-H102 Sec.3 C.
3.3.1.2 Maximum tolerances on CoG and CoB shall be defined with due consideration given to object stability,
criticality and sensitivity of the same during lowering through the wave zone, see [5.2.3.6].
3.3.1.3 The buoyancy and CoB will vary when passing through the splash zone. This shall be taken into
account whenever relevant.
3.3.2 Hydrostatic loads
3.3.2.1 Hydrostatic and differential pressures on submerged objects shall be taken into account.
Guidance note:
Maximum expected external water pressure for objects and compartments should be conservatively assessed. For
lifting equipment (e.g. closed spreader bars) the consequence factor of 1.3 (See DNV-OS-H205 Table 5-1) should be
applied to the maximum pressure.
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3.3.2.2 Objects flooded during submergence shall have sufficient openings to allow the effective escape of air,
considering planned lowering speed.
Guidance note:
It may be necessary to suspend the object for a period of time below water (at a depth unaffected by waves) to allow
complete flooding, before lowering to depth.
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Sec.3 Loads and structural design – Page 28
3.3.2.3 The possibility of entrapped air should be evaluated and included in calculations when relevant. Loss
of stability, risk of implosion and slack slings should at least be investigated.
3.3.3 Environmental loads
3.3.3.1 Environmental loads should be determined, based on the defined environmental conditions, see [2.1.3].
3.3.3.2 Relevant wave, wind and current loads acting on installation vessel(s) and object(s) should be
considered as described in DNV-OS-H102 Sec. 3 D and E.
3.3.3.3 Hydrodynamic loads should be calculated according to DNV-RP-H103.
3.3.4 Accidental loads
3.3.4.1 Possible accidental loads shall be considered (see DNV-OS-H102 Sec.3 F for guidance).
3.3.5 Pull-down and pull-in loads
3.3.5.1 Forces on a buoyant object pulled down by a line from the surface, by means of a sheave or similar
device on the seabed, may be computed in accordance with the principles for a subsea lift. For the final lockin stage, see [3.3.5.2].
3.3.5.2 When an object is pulled in/down, into lock-in position on a sea bed structure, the pull force on the
object may be taken as:
Fpd = 1.2 ηct K [N]
where
ηct: characteristic single amplitude vertical crane tip motion, [m]
K: the stiffness of the hoisting system, see DNV-RP-H103 [4.7.6] [N/m]
3.3.5.3 In general, the hoist line should constitute the weak link in the system. The ultimate capacity (MBL)
of attachment brackets, e.g. attachment of hoist line to the object, attachment of sheave to the bottom structure,
etc., should as a minimum be 1.3 times the MBL of the attached line.
Guidance note:
Alternatively, for welded steel structures the above requirement could be documented by calculations showing that
the (plastic) design capacity in ULS of the connection is equal or greater than the hoist line MBL. The main input
parameters are in this case:
— Design load in ULS = 1.0 × MBL of hoist line.
— Steel characteristic resistance, see DNV-OS-H102 Sec.5 A500.
— Material factor, see DNV-OS-H102 Sec. 5 B400.
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3.3.6 Off-lead, side-lead forces and horizontal offset
3.3.6.1 Off-lead and side-lead forces on cranes/lifting appliances should be calculated on the basis of vessel
motions, environmental and operational loads on the object and the resulting inclination of the hoisting line
from the vertical.
3.3.6.2 The horizontal forces or the horizontal offset and corresponding off-lead and side-lead angles relative
to the vertical (as documented) shall be within the specified design values of the crane/lifting appliance.
Guidance note 1:
Off-lead and side-lead forces are forces on the lifting system occurring when the lifted object is pulled away from the
vertical through the crane tip. Off-lead means in the direction away from the crane, side-lead being perpendicular to
the direction of the crane boom.
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Guidance note 2:
For an axially stiff cable with negligible bending stiffness the offset of a vertical cable with a heavy weight at the end
of the cable in an arbitrary current with unidirectional velocity profile may be calculated according to DNV-RP-H103
[5.2.2.1].
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3.3.7 Loads during positioning
3.3.7.1 Loads related to translation and rotation of the object during lowering, positioning and setting should
be considered, see [7.2].
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Sec.3 Loads and structural design – Page 29
3.3.7.2 Reaction forces from the soil should be determined and accounted for. See Sec.7.
Guidance note:
Such loads may be foundation reactions at seabed impact and suction forces, if an object needs to be recovered or
repositioned.
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3.3.7.3 Both ULS and ALS loads from the guiding and positioning systems shall be defined as found
applicable, see also [2.6.3] and [2.6.4].
3.3.8 Other loads
3.3.8.1 When relevant, due consideration should be given to special loads such as;
—
—
—
—
—
—
tugger line loads
loads due to redistribution of ballast,
loads due to CoG changes
entrapped air
entrapped water
other relevant loads.
3.4 Structural design
3.4.1 General
3.4.1.1 General recommendations regarding structural design and fabrication are given in DNV-OS-H102.
3.4.2 Object
3.4.2.1 Adequate structural strength should be documented for the object involved in the subsea operation.
3.4.2.2 Lifted objects should be designed to withstand hydrostatic, hydrodynamic and any other loads
experienced during transportation and installation, as described in Section [3.3.1] to [3.3.8].
3.4.2.3 Appropriate consequence factors, see DNV-OS-H205 [5.1], should be applied to lift points, primary
and secondary structural elements.
3.4.2.4 Due consideration should be given to skew load cases, the effects of which are not normally covered
by in service design conditions.
3.4.2.5 Attention should be given to possible horizontal load components acting on the lift points.
3.4.3 Bumpers and Guides
3.4.3.1 Bumpers and guides should be designed according to requirements in DNV-OS-H101 Sec.6 C.
3.4.3.2 The maximum entry speed of the object onto the guiding system shall be defined taking into account
the characteristics loads as described in DNV-OS-H101 Sec.6 C200.
3.4.4 Rigging lay down and securing
3.4.4.1 Requirements for design of rigging lay-down and securing arrangements are given in DNV-OS-H205
[5.1.8].
3.4.5 Seafastening and supporting structures
3.4.5.1 Requirements for design of seafastening and vertical support structures (grillage) for transportation of
objects are in general covered in DNV-OS-H202.
3.4.5.2 The seafastening and grillage should allow for easy release and provide adequate support and
horizontal restraint until the object can be lifted clear of the transportation vessel/barge.
3.4.5.3 Elements providing horizontal and/or vertical support after cutting/removal of seafastening shall be
verified for the environmental conditions applicable for the operation.
3.4.6 Inspection
3.4.6.1 Inspection of lift points and lifting equipment should comply with the requirements relating to “special
structural steel” in DNV-OS-H102 Sec.6 B.
3.4.6.2 Lift points shall be inspected for each subsequent lift.
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Sec.3 Loads and structural design – Page 30
Guidance note:
The extent of inspection should be defined based on the available information about the lift point load history and the
original NDT. If no relevant information is available the inspection should be as for a new lift point, see [3.4.6.1]. Lift
points can be accepted for subsequent lifting based on a visual inspection only if;
a) the load history (since last MPI/UT inspection) of the lift points is known,
b) no excessive or uncontrolled loading of the lift points has occurred, or is suspected to have occurred during
previous lifts, and
c) no damages are detected during the visual inspection.
Lift points satisfying items b) and c) only, should be subject to 100% MPI before any subsequent lifting.
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3.4.6.3 Requirements for inspection of objects stored subsea should be agreed before lifting. Demonstration
of appropriate load history since the most recent NDT is normally required.
Guidance note:
See DNV-RP-H102 for specific guidance regarding removal of objects.
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Sec.4 Loadout and transport – Page 31
SECTION 4 LOADOUT AND TRANSPORT
4.1 General
4.1.1 Application
4.1.1.1 The requirements in DNV-OS-H201 and DNV-OS-H202 generally apply for loadout and transport
operations.
4.1.1.2 For load-out by lifting, requirements in DNV-OS-H205 generally apply.
4.1.1.3 This section should be considered as additional and/or clarifying requirements for objects and
operations that are not covered by the conventional load-out and vessel transports methods in the referenced
VMO-standards.
Guidance note:
The following operations and products/objects are covered in this Section:
— Towing of submerged small volume structures and long slender elements.
— Loadout and towing of bundles.
— Loadout and transport of pipelines, risers, cables and umbilicals transported on reels or carousels.
— Load-out and transport of pipe joints.
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4.2 Submerged towing
4.2.1 General
4.2.1.1 Recommendations in this sub-section are applicable for towing of submerged small-volume structures
and long slender elements.
Guidance note:
Three different tow configurations are covered in this sub-section:
— Submerged tow of objects attached to Vessel
— Submerged tow of objects attached to Towed Buoy
— Surface or sub-surface tow of long slender elements (see also [4.3] which covers pipe bundles).
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4.2.1.2 The operation reference period (TR) for the towing operation shall be assessed taking into account the
following:
4.2.1.3 Safe conditions before and after the tow shall be clearly defined.
4.2.1.4 The low towing speed that is normally expected for submerged towing.
4.2.1.5 Considering TR, the operation shall be classified as weather restricted or weather unrestricted, see
DNV-OS-H101 Sec.4.
4.2.1.6 All parameters that could be critical shall be considered during the modelling and analysis of a
submerged tow. See DNV-RP-H103 [7.3.2] for examples of critical parameters.
4.2.2 Submerged tow of objects attached to installation vessel
4.2.2.1 Design considerations for submerged tow of object attached to installation vessel are given in DNVRP-H103 [7.3.3].
4.2.2.2 Hang-off rigging shall be designed in accordance with DNV-OS-H205 Sec.4.
4.2.2.3 Possible fatigue of hang-off point(s) on vessel and lift points / elements supporting lift points on towed
object shall be considered.
4.2.2.4 Possible fatigue of components on towed object, e.g. internal piping, due to VIV shall be considered.
4.2.2.5 Measures shall be taken to prevent abrasion of hang-off rigging and any anti-rotation line(s).
4.2.3 Submerged tow of objects attached to towed buoy
4.2.3.1 Design considerations for the submerged tow of an object attached to towed buoy are given in DNVRP-H103 [7.3.4].
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Sec.4 Loadout and transport – Page 32
4.2.3.2 Design of the towing arrangement shall comply with the requirements in DNV-OS-H202 Sec.4.
4.2.3.3 Hang-off rigging between the buoy and the object shall be designed in accordance with DNV-OSH205 Sec.4. The possibility of fatigue should be considered.
4.2.4 Surface or sub-surface tow of long slender elements
4.2.4.1 Examples of slender objects that can be towed to field are;
— pipelines, bundles, spools
— TLP tethers
— riser towers / hybrid risers.
4.2.4.2 Design considerations for surface or sub-surface tow of long slender elements are given in DNV-RPH103 [7.3.5].
Guidance note:
Several slender objects can be towed as a bundle arrangement (e.g. strapped together or within a protective casing).
[4.3] covers load-out and transport of pipe bundles, however these requirements can also be applicable to other types
of slender objects as outlined in [4.2.4.1].
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4.2.5 Loads and analyses
4.2.5.1 The modelling and analysis of submerged tows should be performed according to the
recommendations in DNV-RP-H103 [7.3.9].
4.2.5.2 All relevant vessel headings shall be analysed, see [3.2.2] for requirements and guidance.
4.2.5.3 All possible (relevant) loads and their appropriate characteristic value shall be identified according to
the principles in Sec.3.
4.2.5.4 Calculated characteristic values of loads should have maximum 10% probability of being exceeded. In
order to verify that the corresponding design load is adequate it is recommended to also check the tail of the
distribution.
Guidance note:
E.g. the 1% probability of being exceeded load could be calculated and verified against the design load and the overall
structural safety requirement, see DNV-OS-H101 Sec.1 A200.
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4.2.5.5 Acceptable clearances to vessel side or moonpool sides should normally be documented by
calculations.
4.3 Bundles
4.3.1 General
4.3.1.1 This sub-section covers controlled depth tow and off-bottom tow of pipe and riser bundles.
4.3.1.2 The bundle design should be based on direct calculation of required bollard pull.
4.3.1.3 Bundle towing connections and wires should be designed based on dynamic analysis of the launch,
towing and holdback forces.
4.3.1.4 Appropriate design factors should be defined with reference to the following alternatives:
— As for towing (DNV-OS-H202) if the object is floating in a controllable manner after a structural and/or
towline failure.
— As for lifting (See Sec.5 and DNV-OS-H205) if the object is not controllable after a structural and/or
towline failure.
4.3.1.5 Bundle break-out forces shall be conservatively estimated. The effects of launch track slope/
settlement, mechanical resistance, launch bogie / roller condition and other relevant parameters that influence
the break out force shall be considered.
4.3.1.6 The stability of the total bundle and tow heads/structures shall be calculated for all stages of the launch,
tow installation and flooding. Side current forces, hydrodynamic effects during tow and free surface effects
during flooding operations should be considered.
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Sec.4 Loadout and transport – Page 33
4.3.1.7 Bundle behaviour during tow should as far as possible be estimated during design. Inline structures
should as far as possible be designed in a way that will minimise the generation of hydrodynamic drag and lift
forces that could cause an instable/fluctuating bundle configuration during tow.
4.3.1.8 Sensitivity studies shall be carried out for essential parameters such as weight, ballast, buoyancy,
salinity, cross current, towing speed, back tension, internal pressure loss etc. for relevant phases.
4.3.2 Load-out of bundles
4.3.2.1 Local environmental conditions at the launch site, such as wave directions/patterns, tide and current
forces should be considered.
4.3.2.2 The launch area, including an adequate corridor to allow for the necessary deflection of bundle, shall
be surveyed prior to the operation.
4.3.2.3 Bundle deflection due to side current shall be analysed for different stages of the launch. The towing
vessel offset positions required to counteract the predicted bundle deflection shall be established.
Guidance note:
When a bundle is towed in its axial direction in an “off-bottom tow mode”, friction between the ballast chain and
seabed cannot be used to counteract lateral deflection of the bundle.
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4.3.2.4 Bundle support and bending restrictions shall be defined, based on structural pipe analysis,
consideration of local soil conditions, the launch track characteristics and bundle weight and stiffness. Variable
conditions such as scour and erosion in wave effected zone and consolidation of the soil shall be considered.
Acceptable departure angles from launch way, in both horizontal and vertical direction, shall be defined.
4.3.2.5 Adequate means of monitoring environmental conditions and limiting load-out parameters shall be
established and tested before commencement of load-out.
4.3.3 Towing of bundles
4.3.3.1 Adequate means of monitoring environmental conditions, tow parameters and bundle configuration
shall be established and tested before commencement of tow.
4.3.3.2 Adequate back-up systems shall be available.
4.3.3.3 The tow route, including an adequate corridor to allow for the necessary deflection of bundle and
temporary lay-down areas, shall be surveyed prior to start of tow.
4.3.3.4 Prior to commencing the tow the bundle shall be ballasted to an acceptable configuration for the tow
4.3.3.5 Bundle parameters, configuration and feedback shall be systematically checked after commencement
of the tow. Deviations from expected values shall be recorded and any possible effects on the towing procedure
and bundle evaluated.
4.3.3.6 Bundle deflection and anchorage forces (required to stabilise the bundle in any predefined holding
locations) shall be analysed for the characteristic current conditions and loads.
4.3.3.7 Current speed (and direction) should be monitored at regular intervals during tow and holding periods,
unless extreme current values are used in the analysis of bundle behaviour. Contingency procedures should be
available and mitigating actions employed in case the current speed exceeds the design values.
4.3.3.8 Bundle behaviour following towline failure should be assessed and used as a basis for evaluating and
generating and appropriate contingency procedures.
Guidance note:
Qualification testing should be based on a product and configuration representative of the actual bundle and towing
conditions anticipated.
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4.3.3.9 The strength of the bundle should be documented as adequate for all potential situations, including that
where it is hanging freely supported only at each end.
4.3.3.10 If external ballast is used (normally chain) the bundle must be sufficiently robust to accept some loss
of ballast during tow, without undue effect on the bundle configuration.
4.3.3.11 Adequate abandonment equipment shall be carried on-board the lead tug(s) and trailing tug, to enable
controlled laydown and abandonment if necessary.
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Sec.4 Loadout and transport – Page 34
4.4 Pipelines, risers, cables and umbilicals
4.4.1 General
4.4.1.1 This subsection applies to pipelines, risers, cables and umbilicals transported on (and installed from)
reels or carousels. Relevant requirements are also applicable for products transported on (and installed from)
baskets.
4.4.1.2 Requirements for load-out/shore pull including reeling of pipe strings (‘stalks’) are covered in DNVOS-F101 Sec.10 F700 and Sec.10 F400 (if applicable).
Guidance note:
Guidance regarding loadout and transport of cables can also be found in DNV-RP-J301 [5.3].
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4.4.2 Load out by lifting
4.4.2.1 Lifting equipment shall comply with the requirements in DNV-OS-H205.
4.4.2.2 Heavy items, structures and end terminations stored with the product can influence the CoG of the reel/
basket/carousel significantly and shall be taken into account when undertaking the design for lifting and
transportation.
4.4.3 Load-out by spooling
4.4.3.1 An operation-specific procedure for the load-out operation shall be prepared, including a detailed
description of the planning and step-by-step procedure for the execution of spooling itself.
4.4.3.2 Spooling operations shall be designed such that the associated handling procedures do not result in
tension, twisting or bending of the product (including terminations and ancillary equipment) in excess of its
operational limitations.
4.4.3.3 Continuous monitoring of the tension, pulling force and other relevant parameters by means of
measuring devices shall be performed during spooling; the accuracy required is given in DNV-OS-H101 Sec.4
D.
4.4.3.4 Critical steps in the spooling operation should be visually monitored continuously, including transition
points (rollers, deflectors, sheaves, chutes, spans etc.) to monitor for the presence of excessive twist - the
maximum allowable twist shall be defined.
4.4.3.5 Product lift/transfer arrangements and procedures shall be designed so that product limiting criteria are
not exceeded. Tension shall be maintained in free spans such that the resulting catenary does not infringe the
minimum bending radius defined for spooling operations.
Guidance note:
The product may be supported at each end by bend shoes, sheaves, chutes or bellmouths of a suitable radius.
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4.4.3.6 Any lifting gear/equipment and attachment points shall be configured such that the product remains
within all its design limiting criteria.
4.4.3.7 Lifting equipment used to handle in-line and end structures / end terminations shall be designed in
accordance with DNV-OS-H205 Sec.3. The design of lifting equipment and lift points on such structures
should consider all possible load directions and distributions between different parts of the rigging.
4.4.3.8 Methods involving for example soft slings, Chinese fingers or similar choked around the product, used
for pulling and/or hold-back of the product, shall be qualified prior to operation. Qualification should include
testing carried out on a configuration representative of the actual product and load conditions/directions.
4.4.3.9 The design of load-out vessel moorings should consider reaction loads during the spooling operation.
Vessel mooring design should consider tidal range, necessary offsets and heading variations, with reference to
pipe spans and allowable product loads.
4.4.3.10 Operators of the spooling units (winches, carousel, turntable, etc.) shall be in continuous radio
contact. Spare radio sets shall be available.
4.4.4 Sea transport
4.4.4.1 All products, including in-line assemblies, end structures/terminations, buoyancy modules, clamps and
other accessories shall be seafastened according to requirements in DNV-OS-H202.
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Sec.4 Loadout and transport – Page 35
4.4.4.2 The structural integrity of equipment such as reels, carousels and baskets shall be documented as
adequate. The actual transport condition and product parameters including, but not limited to, for example
content, packing arrangements, ‘locked-in’ spooling tension, CoG, load distribution and weight/length
contingency shall be considered.
4.4.4.3 When transport is on board the installation vessel and the installation equipment also acts as
permanent/temporary seafastening, e.g. reel drive systems, the mechanical/hydraulic capacity of the
installation equipment shall be documented as sufficient for the relevant transportation loads. Special attention
should be given to systems depending on hydraulic pressure, gears and roller/bearing systems exposed to high
loads in a static condition.
4.4.4.4 The seafastening arrangements for storage reels not supported in a reel-drive system should be
documented for all phases.
Guidance note:
A seafastening release procedure should document that the reel is adequately secured until the reel drive system is
mounted.
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4.5 Pipe joints
4.5.1 General
4.5.1.1 This subsection is applicable to the load-out and transport of individual and multiple pipe joints.
Guidance note:
A pipe joint is a length of steel pipe, approx. 12 m long, used in the manufacturing of offshore pipelines. A double
joint consist of two pipe joints welded together, reducing the number of offshore welds and thereby the offshore
installation time.
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4.5.2 Load out by lifting
4.5.2.1 Handling and lifting of pipe joints shall be performed according to recognised procedures and methods.
Equipment used for handling and lifting shall be designed to prevent damage to coatings and/or prepared pipe
ends.
4.5.2.2 The capacity of lifting equipment shall comply with requirements in DNV-OS-H205.
4.5.3 Sea Transport
4.5.3.1 All products, including pipe joints, in-line assemblies, end structures/terminations and other
accessories shall be seafastened following the principles in DNV-OS-H202.
4.5.3.2 Acceptable stacking heights shall be established and documented for transportation loads. Each pipe
joint and pipe stack shall withstand relevant weight and environmental loading. Drainage of water shall be
ensured. Potential icing shall be considered and appropriate measures should be taken where necessary.
4.5.4 Offshore pipe loading
4.5.4.1 Pipe loading offshore shall not be done in areas where a pipe dropped overboard could damage
pipelines or other subsea assets, see DNV-OS-H102 Sec.3 F303 for guidance on the safe distance required.
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Sec.5 Subsea lifting – Page 36
SECTION 5 SUBSEA LIFTING
5.1 General
5.1.1 Application
5.1.1.1 Requirements for lifting in air (see DNV-OS-H205) are generally also applicable to subsea lifting
operations.
5.1.1.2 Subsea lifting is defined as installing, moving or recovering an object subsea by means of a crane or
other lifting appliance.
5.1.1.3 General requirements for subsea operations are given in Sec.2. The following sub-sections should be
considered as additional/supplementary requirements for subsea lifting operations.
5.2 Loads and analysis
5.2.1 Loads
5.2.1.1 General requirements are given in Sec.3; all loads relevant to a subsea lift shall be taken into account.
5.2.1.2 Both minimum and maximum values should be applied in calculation of static weight, ref. DNV-RPH103[4.2.2].
Guidance note:
Variation in weight/mass due to flooding/draining of subsea structures as described in DNV-RP-H103 [4.2.2] should
not be considered as accidental conditions and the associated loads are hence applicable in ULS loadcases.
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5.2.1.3 The estimation of hydrodynamic coefficients should follow the recommendations given in DNV-RPH103 [4.6]. See also DNV-RP-C205 for guidance.
5.2.1.4 The stiffness of the hoisting system can be calculated according DNV-RP-H103 [4.7.6].
5.2.1.5 If unavoidable, snap loads shall be analysed thoroughly.
Guidance note 1:
If the hoist line or one or more slings become slack, significant snap forces may be experienced. A slack condition
normally occurs if the hydrodynamic forces exceed the force caused by the static (submerged) weight of an object.
Appropriate limiting weather conditions should be defined where possible such that slack sling criteria are fulfilled
and snap loads are avoided, see [5.3.1.1].
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Guidance note 2:
Characteristic snap loads may be calculated according to DNV-RP-H103 [4.7.2] or by more advanced methods, see
e.g. [5.3.2.4].
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5.2.2 Combination of loads
5.2.2.1 An appropriate and structured method of combining all relevant loads shall be used. See DNV-OSH102 and DNV-RP-H103 for requirements and guidance.
Guidance note:
If time domain analyses are applied, various combinations of irregular waves (wind seas) and swell may be included
for direct calculation of combined load effects and the resulting forces on the lifted object.
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5.2.3 Lift analysis - General
5.2.3.1 Lifts shall be analysed for all relevant loadcases. See DNV-OS-H102 Sec. 4 for general requirements.
5.2.3.2 Adequate control of the lift in air should if necessary be documented by analysis. See DNV-OS-H205
[2.3.2].
Guidance note:
The formula presented in DNV-RP-H103 [9.2.1.6] can be used to check if horizontal resonance is likely to occur. If
such amplification can occur it should be documented by calculations/analysis that horizontal motions are prohibited
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Sec.5 Subsea lifting – Page 37
by physical means (DNV-OS-H205 [2.3.2.1]). Note also that spreader bars and/or crane hooks can be subject to
critical (double) pendulum motions.
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5.2.3.3 All critical vertical positions of the object relative to the sea surface shall be included in the lift
analysis. See DNV-RP-H103 [4.5] for further guidance.
5.2.3.4 If clearances during deck handling operations are considered critical, see [5.6.1.4], lift off from the
deck of the installation vessel should be analysed to estimate the minimum clearances between the lifted object
and other structures/vessel side.
5.2.3.5 If tugger wires are used to control a lifted object, the required capacity of the tugger wire arrangement
should be calculated; both the winch wire tension and winch pay-out/pay-in speed should be considered.
5.2.3.6 The lifted object shall be documented as having adequate stability when lowering through the wave
zone. See [2.5.2.3].
5.2.3.7 Hydrodynamic forces on objects lowered through the water surface and below the wave influenced
zone, can be estimated using the simplified method described in [5.2.4]. Other methods may be applicable, see
[5.4].
5.2.3.8 The local strength of lifted equipment (including hatch covers, ancillary equipment, etc.) should be
checked for the effects of wave slamming.
5.2.3.9 Guidance for estimating loads associated with deepwater operations is given in Section [5.7.1].
5.2.3.10 Positioning loads are covered in [3.3.7], whilst geotechnical aspects related to landing on and retrieval
from the seabed are covered in Sec.7.
5.2.3.11 It shall be documented that for landing operations relying on active heave compensation (AHC), the
crane tip heave motion and heave velocity remains within the compensating capacity of the AHC system. See
also [2.4.2].
5.2.4 Simplified method for estimation of hydrodynamic forces acting on submerged objects
5.2.4.1 The Simplified Method described in DNV-RP-H103 [4.3], may be used to estimate the forces on
objects lowered through the water surface and down to the seabed. The method is equally applicable for
retrieval.
5.2.4.2 The intention of the Simplified Method is to provide a basic, albeit conservative, estimate of the forces
acting on a lifted object. Alternative calculation methods can be considered acceptable provided they follow
the general guidelines given in [5.4].
5.2.4.3 The Simplified Method may be adopted assuming the following criteria are fulfilled:
— The size of the lifted object (overall length) is relatively small compared to the wave length.
— The vertical motion of the object follows the crane tip motion.
— The load case is dominated by relative vertical motion between object and water – other modes of motions
can be disregarded.
Guidance note 1:
The horizontal extent of the lifted object (in the wave propagation direction) should be less than 1/4 of the typical
wave lengths of the waves exciting the structure. The force in the hoist line will normally be conservatively estimated
if the horizontal extent of the lifted object is larger than the above limitation. Forces experienced in individual slings
however can be underestimated as unsymmetrical loading can be more pronounced for larger objects.
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Guidance note 2:
The method is not applicable if the crane tip oscillation period or the wave period is close to the resonance period of
the hoisting system. For further guidance see DNV-RP-H103.
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Guidance note 3:
Note that the lifted object may be divided into main items and surfaces contributing to the hydrodynamic force, see
DNV-RP-H103 [4.3.9.6].
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5.2.4.4 More accurate estimations are required if the criteria in [5.2.4.3] are not fulfilled, see [5.4].
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Sec.5 Subsea lifting – Page 38
5.3 Acceptance criteria
5.3.1 Acceptance criteria – Simplified method
5.3.1.1 The following criterion should be fulfilled in order to ensure that snap loads are avoided in the slings
and hoist line:
Fhyd ≤ 0.9 × Fstatic-min [N]
where
Fstatic-min
Fhyd
= Force due to minimum static weight of object [N], see [5.3.1.2].
= Characteristic hydrodynamic force [N]
Guidance note 1:
A 10% margin to the start of slack slings is assumed to be an adequate safety level given the load factors and
combinations stated in the ULS criteria.
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Guidance note 2:
When deploying objects that are close to neutrally buoyant (e.g. ROVs, etc) it will normally not be possible to fulfil
the slack sling criteria in moderate sea states. In such cases the hoisting system should incorporate a guide system to
ensure controlled clearance from the vessel side. Further, unless means to avoid snap loads are available, the
characteristic snap load should be accounted for in the design. The characteristic snap load may be calculated
according to DNV-RP-H103 [4.7.2].
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5.3.1.2 The minimum static weight of an object as described in [5.2.1.2] should be applied when checking
slack sling criterion.
5.3.1.3 In addition to the slack sling criterion, the capacity of lifted object and lifting equipment should be
checked according to DNV-OS-H205.
5.3.1.4 The Characteristic total force on an object should be established by applying the maximum static
weight, see [5.2.1.2].
5.3.1.5 The capacity checks described in DNV-OS-H205, Lifting Operations, relate to the weight of the object
in air. Hence, a converted dynamic amplification factor (DAF) should be applied equivalent to a factor valid in
air. The following relation should be applied in the equations given in DNV-OS-H205:
DAFconv = Ftotal / mg
where
DAFconv
m
g
Ftotal
Fstatic-max
=
=
=
=
=
is the converted dynamic amplification factor
mass of object in air [kg]
acceleration of gravity = 9.81 [m/s2]
is the largest of: Ftotal = Fstatic-max + Fhyd or Ftotal = Fstatic-max + Fsnap [N]
Force due to maximum static weight of object [N], see [5.3.1.4].
5.3.1.6 The base case method in DNV-OS-H205 [5.1.2] should be used to define the load factors (and the
design load) only if the Simplified Method is applied.
5.3.2 Acceptance criteria - Alternative
5.3.2.1 Acceptance criteria in this paragraph are applicable if the methods described in [5.4] are used to
calculate hydrodynamic forces.
5.3.2.2 Acceptance criteria in [5.3.1] (for avoidance of snap loads) are applicable for the main hoist line. For
individual slings Fhyd ≤ 1.0 ⋅ Fstatic-min is acceptable.
5.3.2.3 The capacity of lifted object and lifting equipment shall be checked as indicated in [5.3.1.3], [5.3.1.4]
and [5.3.1.5].
5.3.2.4 Snap loads may be established using time domain analyses; this requires appropriate and accurate
modelling of hoisting system and lift rigging characteristics.
5.3.2.5 The probability of exceeding the calculated extreme characteristic load (hydrodynamic + static load or
snap load) in the operation period shall not exceed 10%. In order to verify that the corresponding design load
is adequate it is recommended to also check the tail of the distribution. See [4.2.5.4] GN.
5.3.2.6 The design load could be calculated based on the two ULS load conditions “a” and “b”. See DNV-OSH102 Sec.5 B (and DNV-OS-H205 [5.1.3]). Note that the load factors shall be applied to the characteristic
hydrodynamic and static loads acting on the object.
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Offshore Standard DNV-OS-H206, September 2014
Sec.5 Subsea lifting – Page 39
Guidance note:
The acceptance criterion in [5.3.1.1] is assumed to provide an adequate safety level given the load factors and load
combinations stated in the ULS criteria. If slack slings are encountered, the design loads should preferably be
calculated as indicated. However, the alternative given below in [5.3.2.7] can be found acceptable.
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5.3.2.7 If the approach in [5.3.2.6] is not followed, a load factor of 1.3 shall be applied on the total
characteristic lift force including snap load (i.e. characteristic static load + characteristic dynamic load). See
also GN above.
5.4 More accurate estimation of hydrodynamic forces
5.4.1 General
5.4.1.1 If the criteria for using the simplified method, given in [5.2.4], are not fulfilled or more accurate
calculation methods are desired, alternative calculation methods can be acceptable, providing they follow the
recommendations given in DNV-RP-H103 [3.4].
5.4.1.2 See [5.3.2] for accept criteria.
5.4.2 Documentation
5.4.2.1 General requirements for documentation are given in [2.2]. If alternative calculation methods are used,
additional documentation as described in this sub-section shall be made available.
5.4.2.2 Documentation based upon regular design wave approach should be comprehensively and thoroughly
described, such that the calculations are reproducible.
5.4.2.3 As a minimum, for time domain analyses the following documentation is required:
— Description of how the hydrodynamic model of the vessel has been derived, load condition, etc.
— Description of how the object’s hydrodynamic coefficients have been derived. Values should be included
for both individual elements and the total added mass/damping.
— Description of how slamming has been modelled, comparison of slamming loads versus analytical results,
results from model tests or CFD analyses.
— Description of how extreme forces have been estimated.
5.4.2.4 As a minimum for CFD analyses, the following documentation is required:
—
—
—
—
—
—
Numerical method applied.
Applied boundary conditions and size of computational domain.
Applied turbulence model.
Results from spatial and temporal convergence tests.
Description of how transient effects are accounted for.
Computed forces, pressures and velocities should be checked and compared with approximate hand
calculations.
5.4.2.5 If model test results are available, numerical simulation results should be compared and validated with
the model test.
5.5 Lifted object
5.5.1 General
5.5.1.1 Requirements for the structural design of lifted objects are given in [3.4].
5.5.1.2 DNV Standard for Certification No 2.7-3 may be used as an alternative standard for structural
verification of objects lifted subsea.
Guidance note:
DNV Standard for Certification No 2.7-3 covers all objects defined as portable offshore units and it is recommended used:
— where units are intended to be transported, lifted and installed repeatedly
— and/or for units where generic handling procedures are intended to be used
— and/or for units that require certification.
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Sec.5 Subsea lifting – Page 40
5.5.2 Pipelines, risers, cables and umbilicals
5.5.2.1 For objects that are partly supported by a lifting appliance, the load distribution on the object shall be
thoroughly evaluated.
5.5.2.2 Loads for risers, umbilicals and cables are generally covered in [6.4.1]. Relevant loads and analytical
methods should consider possible (dynamic) effects due to the geometry of the termination.
5.5.2.3 The lifting structure shall fulfil the requirements for structural design given in Sec.3.
5.5.2.4 Additional loads due to handling and positioning of end termination assemblies shall be considered.
Guidance note:
Riser-like products will normally be fitted with termination assemblies designed for subsea installation by lifting,
seabed support and for tie-in. Such termination assemblies can be difficult to position due to the lateral, vertical and
rotational stiffness of the product attached.
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5.5.3 Spools
5.5.3.1 Spools are typically slender structures, with concentrated masses at the ends. Relevant loads and
analyses methods should be adopted to consider possible dynamic effects associated with such geometry.
5.5.3.2 For objects with large horizontal extent e.g. long slender structures like spool pieces, spreader beams,
etc. more refined analyses (than the Simplified Method described in [5.2.4]) are needed to adequately establish
loads in individual slings.
5.5.3.3 Local reaction forces at support points should be considered.
5.5.3.4 Free flooding of objects such as spools, spreader beams, etc. can cause large shifts in CoG, subsequent
instability and possible overturning. These effects should be duly considered.
5.5.3.5 Trial lifting of spools and/or jumpers shall be carried out to verify the rigging geometry prior to loadout. If the trial lift reveals that a sling is slack or the tilt angle is unacceptable, sling lengths shall be adjusted
and the test lift repeated.
5.5.4 Retrieval of damaged objects
5.5.4.1 The status and integrity of a damaged object shall be established prior to retrieval, to avoid collapse
and further damage during recovery.
5.5.4.2 In many cases objects are not designed for retrieval loadcases in a damaged state, hence applicable
retrieval load cases, taking into account water filling, soil forces, suction, grouting, marine growth, etc. shall
be considered.
5.5.4.3 The loads experienced by a damaged object during retrieval and re-installation can affect its future
fatigue resistance and design life. This shall be reduced accordingly.
5.6 Operational aspects
5.6.1 General
5.6.1.1 See [2.10] for general requirements relating to the planning and execution of subsea operations.
5.6.1.2 Operational aspects for all phases of the subsea lift operation shall be considered.
Guidance note:
A typical subsea lift consists of the following main phases/steps:
— removal / release of seafastening
— lift-off from deck and manoeuvring object clear of transportation vessel/barge
— lowering through the wave zone
— lowering to seabed
— positioning and set-down
— disconnect and retrieve lift rigging.
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5.6.1.3 In addition to the onshore test lift described in [2.5.6], a trial over boarding lift during mobilisation is
recommended to: verify available hook height, confirm that the intended lift path is free from obstructions,
confirm clearances to other objects/vessel side, check routing of tugger lines/tag lines, etc.
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Offshore Standard DNV-OS-H206, September 2014
Sec.5 Subsea lifting – Page 41
5.6.1.4 The operational aspects for lift operations in air, see DNV-OS-H205 [2.3] are normally applicable also
for subsea objects.
Guidance note:
[2.3] in DNV-OS-H205 includes recommendations for:
— control of lift
— clearances
— lifting (operational criteria and procedure details)
— monitoring of lifting operations
— cutting of seafastening.
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5.6.1.5 When lifting an object from a barge or other vessel on board a crane vessel positioned side by side, the
relative motion between the crane hook and the barge at the position of the lifted object is critical. The risk of
interference between barge/vessel and the lifted object after lift-off should be considered.
5.6.1.6 Assumptions, see [5.2.3.6], regarding stability of an object should be considered during lowering
through the wave zone. This can be particularly relevant in relation to:
— tilting of partly air-filled objects during lowering
— the effect of free water surface inside an object
— the possibility of entrapped air.
5.6.1.7 During lowering of an object to the seabed the following should be considered:
— Horizontal offset due to current (where the current velocity can be time-dependent and its magnitude and
direction variable with water depth).
— Dynamics and possible resonance effects due to wave induced motion of crane tip on vessel.
5.6.1.8 The object’s maximum allowable landing velocity shall not be exceeded, regardless of whether the
structure is landed onto the seabed or another structure.
Guidance note:
Landing velocity is the sum of the objects vertical heave velocity and the crane/hoisting system pay-out speed.
Adjustment of the weather criteria might be necessary to limit the landing velocity.
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5.6.2 Installation tolerances
5.6.2.1 Installation tolerances shall be clearly defined. The means for controlling and ultimately confirming
these shall be available.
5.6.2.2 The feasibility of achieving the installation tolerances should be thoroughly reviewed based on factors
such as:
—
—
—
—
—
—
—
—
—
experience from similar operations
manufacturing tolerances
dimensional control surveys
trial fits
environmental conditions
ability to assist positioning of the object by use of guiding or orientation systems
soil conditions
expected visibility
accuracy of survey/measuring equipment.
5.6.2.3 Once the correct installation position has been confirmed, the lift rigging should be disconnected
without undue delay. ROV (or diver) access and snag free release of lift rigging are critical aspects that should
be considered early in the design process.
5.6.3 Wet parking
5.6.3.1 The seabed condition shall be assessed if wet parking is planned or included in contingency procedures.
The need for seabed preparation shall be evaluated.
5.6.3.2 Assessment of seabed condition should normally include calculations of soil capacity, on-bottom
stability and if relevant necessary break-out forces due to suction.
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Offshore Standard DNV-OS-H206, September 2014
Sec.5 Subsea lifting – Page 42
Guidance note:
The maximum length of time that the structure could be wet stored should be considered. Assessments should evaluate
likely seabed penetrations. Further guidance for calculating these effects are given in Sec.7.
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5.6.4 Safety and contingency
5.6.4.1 General requirements for contingency planning are given in [2.10.6].
Guidance note:
Typical contingency situations can relate to damage of lifted object due to unexpected loads, failure of vessel
positioning system, failure of object guiding and/or positioning system, out of tolerance installation position, failure
of crane, failure of lift rigging, ROV breakdown, deteriorating weather conditions or any other contingency situation
identified from risk identifying activities.
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5.6.4.2 Contingency procedures shall, where necessary, consider and address whether the object could be
temporarily abandoned on seabed, temporarily suspended or recovered to deck of the installation vessel.
5.7 Deep water
5.7.1 Deep water lowering operations
5.7.1.1 For lifting operations in deep water the following effects shall be considered:
— Cable stretch due to self-weight and weight of lifted object.
— Horizontal offset due to current where the current velocity can be time-dependent and its magnitude and
direction can vary with water depth.
— Dynamics and possible resonance effects due to wave induced motion of vessel crane tip.
— Methods for controlling vertical motion of lifted object.
Guidance note:
See DNV-RP-H103 Sec. 5 for advice on how to calculate these effects. Note also that deep water is not specified as
a specific limit in this Standard as a reasonable fixed limit will depend on prevailing environmental conditions and
application, e.g. drilling, diving, subsea construction, renewable energy, etc.
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5.7.1.2 The permissible installation tolerances shall be determined taking into account the increased difficulty
in accurate seabed positioning caused by large water depth and environmental conditions (current).
5.7.1.3 Deep water lowering and landing/docking operations must be planned with due consideration of the
time needed for deployment / recovery of units, tools and ROV’s, for handling, manoeuvring, guiding and
positioning.
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Sec.6 Installation of pipelines, risers, cables and umbilicals – Page 43
SECTION 6 INSTALLATION OF PIPELINES, RISERS, CABLES AND
UMBILICALS
6.1 General
6.1.1 Application
6.1.1.1 This Section gives requirements and guidance for installation of both rigid and flexible submarine
pipeline and cable systems including pipelines, risers, cables and umbilicals. Both static and dynamic
applications are covered.
Guidance note 1:
DNV-OS-F101 Submarine Pipeline Systems Sec.10 gives requirements for installation/offshore construction of
submarine pipeline systems. Parts of DNV-OS-F101 Sec.10 are also generally applicable for flexible pipes and risers.
Hence, requirements in DNV-OS-F101 are widely referred to and/or repeated in this Section where applicable.
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Guidance note 2:
Detailed guidance regarding installation of cables may be found in DNV-RP-J301 Sec. 6. Additional guidance for
wind farm cable installations may be found in ND/0035, Section 10.
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Guidance note 3:
In this section, the installation of submarine pipeline and cable systems including pipelines, risers, cables and
umbilicals is referred to as “laying operations”; “product” is used as a collective term for the various objects covered
in this section.
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Guidance note 4:
Further guidance on subjects not explicitly covered in this Section may be found in ND/0029. Examples are:
— Installation of deep water Steel Catenary Risers (SCR).
— Burial of pipeline by trenching and backfill, jetting, rock placement or dumping.
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6.1.2 Risk management
6.1.2.1 Operational risk should be evaluated and handled in a systematic way. See DNV-OS-H101 Sec.2 C.
6.1.2.2 Risk identification techniques and methods shall be used as applicable for the intended operation, see
DNV-OS-H101 Sec.2 C.
6.1.2.3 The extent of risk evaluations shall depend on the criticality of operations and experience from
previous similar operations. For laying operations risk analyses should normally include a failure mode effect
analysis (FMEA) for equipment and hazard and operability studies (HAZOP) for critical operations.
Guidance note:
Typical items to be covered in HAZOP are:
— simultaneous operations
— lifting operations including pipe joints transportation and storage
— dry and wet buckles including flooding of pipe
— initiation and lay down including shore pull
— operations inside safety zones
— critical operations (laying in short radii curves, areas with steep slopes etc.)
— crossings
— failure of equipment and measuring and monitoring devices
— tie-in operation
— pre-commissioning activities
— environmental conditions and weather criteria
— emergency abandonment
— loss of station keeping capabilities
— survey.
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Sec.6 Installation of pipelines, risers, cables and umbilicals – Page 44
6.2 Operational planning
6.2.1 General
6.2.1.1 General requirements for the planning of subsea operations are given in Sec.2. The following
paragraphs should be considered supplementary for laying operations.
6.2.2 Operation period
6.2.2.1 The required operation reference period, TR, see [2.1.2] should be thoroughly evaluated at an early
stage.
Guidance note:
— Marine operations may either be classified as weather restricted or as unrestricted, DNV-OS-H101 Sec.2 A200.
See also [6.2.3].
— In case operation limits are stricter for ceasing the operation than for normal laying this should be evaluated in
detail and accounted for in the operation planning.
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6.2.3 Continuous operations
6.2.3.1 Laying operations with a planned duration exceeding the limitation for weather restricted operations,
see DNV-OS-H101 Sec.4 B500, may still be defined as such subject to the following conditions:
— Continuous surveillance of actual and forecast weather conditions is implemented.
— The operation can be halted and the handled object brought into Safe Condition within the maximum
allowable period for a weather restricted operation.
Guidance note:
Safe Condition is defined in DNV-OS-H101 Sec.2 A102, GN.
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6.2.4 Safety and contingency
6.2.4.1 General requirements for contingency planning are given in [2.10.6].
6.2.4.2 Detailed contingency procedures for each critical operational step should be established.
Guidance note:
For laying operations typical contingency procedures can include failure of dynamic positioning system, failure of
anchors or anchor lines, coating repair, anode repair, failure of tensioning system, ROV breakdown, breakdown/
failure of position reference systems/ navigation reference system, weather conditions in excess of operating limit
conditions, third party marine activity and critical or emergency situations identified in FMEA or HAZOP studies.
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6.2.4.3 The schedule shall include contingency time for possible repair/s (e.g. of damaged sheathing/coating).
6.2.5 Operation manual
6.2.5.1 General requirements for the content of the operation/installation manual are given in [2.2.3].
6.2.5.2 For laying operations the installation manual content described in DNV-OS-F101 Sec.10 L should be
considered.
Guidance note:
The definition of installation manual in DNV-OS-F101 Sec.10 L is different from the definition applied in the VMOStandard. The definition in DNV-OS-F101 is more comparable with what the VMO-Standard requires for
documentation at site. See DNV-OS-H101 Sec.4 G.
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6.3 Installation spread, aids and ancillary equipment
6.3.1 Installation spread
6.3.1.1 The installation spread for vessels performing installation of products as described in [6.1.1.1] shall
comply with the requirements in DNV-OS-F101 Sec.10 D.
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Sec.6 Installation of pipelines, risers, cables and umbilicals – Page 45
Guidance note 1:
DNV-OS-F101 Sec.10 D gives requirements for:
— vessels
— position reference systems/ navigation reference systems
— anchor systems, anchor patterns, anchor handling
— dynamic positioning
— cranes and lifting equipment
— lay vessel arrangement, laying equipment, instrumentation
— mobilization activities
— qualification of vessel and equipment
— calibration and testing.
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Guidance note 2:
For further guidance regarding installation spread for cables see DNV-RP-J301 [6.2].
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6.3.1.2 The tensioner system shall be qualified for the actual product dimension to be installed. Variations in
outer diameter due to both production tolerances and dimensional transitions shall be within the working range
of the tensioner system.
6.3.2 Calibration and testing
6.3.2.1 Testing and calibration of laying equipment shall be done according to DNV-OS-F101 Sec.10 D.
6.3.2.2 Applicable integration testing should be carried out, see [2.10.4].
6.3.3 Installation aids and ancillary equipment
6.3.3.1 The installation vessel shall carry a sufficient amount of spares for the lay operation, especially for
critical equipment/tools used over and close to vessel side.
6.3.3.2 Temporary product hang-off shall be well planned, using dedicated equipment only. The hang-off
system should normally consist of well supported hang off collar/clamp.
Guidance note:
Product hang off using soft slings, Chinese fingers or similar choked around the product can be accepted if the method
is properly qualified, see [6.3.3.3], prior to operation.
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6.3.3.3 Clamps and other attachment devices shall be qualified. Qualification should include testing carried
out on a configuration representative of the actual product and load conditions/directions.
Guidance note:
When clamping on coating materials with undocumented creep properties/shear properties, an endurance test shall be
included; the holding time should reflect the operational requirements. See [2.5.5] for requirements to lifting tools.
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6.3.3.4 All work in the proximity of the clamping area that could influence material properties or the load, such
as heat, chemicals, grease, vibration, aligning pipe/product with side force etc., shall be specially considered.
6.3.3.5 Clump weights used during initiation or pull down, shall be of suitable weight and design. Sharp edges
that could cause excessive point loads on or abrasion of the product and/or installation rigging shall be avoided.
6.3.3.6 Clamps/swivel joints shall be qualified for the product, configuration and installation method to ensure
correct functioning during all phases. Special attention should be given to self-aligning swivel joints which can
be required to accommodate very different angles under installation and in-place conditions.
6.3.3.7 Emergency hang off facilities shall be readily available at all times. Moving, mounting, operation,
holding capacity and power supply shall be tested and/or documented prior to commencement of the operation.
6.3.3.8 All clamps, protection frames, anchor flanges etc., shall be installed in accordance with the
specification and drawings, using appropriate bolt torque and to the specified tolerances.
6.3.4 Abandonment and recovery system
6.3.4.1 The abandonment and recovery system (A&R) should be able to abandon the product safely if waterfilled. If the recovery system is incapable of recovering the product, alternative methods should be available.
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Sec.6 Installation of pipelines, risers, cables and umbilicals – Page 46
Guidance note:
For Pipe in Pipe systems it is normally acceptable to assume only that the inner pipe or the annulus is flooded, not both.
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6.3.4.2 Rigging components used to attach the A&R winch wire to the product lay-down tool shall be designed
in accordance with DNV-OS-H205 Sec.4. See also [2.7.3.1].
6.3.5 In-line and termination structures
6.3.5.1 This sub-section applies to product in-line structures such as tees, wyes, junction boxes etc. and to
product end terminations/end modules.
6.3.5.2 In-line structures shall incorporate means of preventing overturning caused by pipeline rotation;
structures with their COG above the pipeline centre shall be specially considered.
6.3.5.3 Lifting equipment used to handle in-line and end structures/end terminations shall be designed in
accordance with DNV-OS-H205 Sec.4. The operation shall be planned to ensure that handling of the structures/
terminations does not introduce unacceptable levels of tension, twist or bending into the pipeline/product at the
termination.
6.3.5.4 Design of lifting equipment and lift points on in-line and end structures should consider all possible
load directions and load distribution between the different parts of the rigging.
6.3.6 (Platform) Pull-in winch systems
6.3.6.1 The required capacity of the pull-in winch, winch wire and other parts of the pull-in system should be
based on maximum expected dynamic load during operation and relevant safety factors.
6.3.6.2 The safety factor philosophy shall be based on a consequence analysis. If pull-in wire failure is likely
to result in loss of the pull-in object, a safety factor comparable with the lifting equipment should normally be
used.
6.3.6.3 Winches (including sheaves, blocks, foundations, etc.) used for product pull-in towards platform/other
installations should be commissioned according to approved procedures. See DNV-OS-H101 Sec.4 F.
Guidance note:
Winch commissioning should normally include dynamic load testing with 110% of the maximum expected load
during operation. Testing should be carried out using the number of wire rope layer(s) that will be present when the
maximum expected load occurs.
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6.3.6.4 Rigging components used to attach the winch wire to the product/pull-in head shall be designed in
accordance with DNV-OS-H205 Sec.4. See also [2.7.3.1].
6.4 Loads and design
6.4.1 Loads
6.4.1.1 General requirements for loads are given in Sec.3. All loads relevant for the objects covered in this
section shall be taken into account.
6.4.1.2 A general definition of load categories and description of loads are given in DNV-OS-H102 Sec.3.
Guidance note:
It should be noted that DNV-OS-F101 and DNV-OS-F201 categorize loads somewhat differently to DNV-OS-H102
as indicated below:
— Both G and Q loads are called functional loads in DNV-OS-F101 Sec.4 B.
— E loads have the same definition, i.e. environmental loads - see DNV-OS-F101 Sec.4 C.
DNV-OS-F101 Sec.4 E defines interference loads. These could be considered as accidental loads with probability
greater than 1/10 000 per operation, see DNV-OS-H102 Sec.5 D204.
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6.4.1.3 This section considers loads related to the installation (construction) phases of the product. Loads
related to the operating phases of the product shall be treated in accordance with recognized design codes.
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Sec.6 Installation of pipelines, risers, cables and umbilicals – Page 47
Guidance note:
Construction loads are described in DNV-OS-F101 Sec.4 D and should be categorised as P, Q or E loads.
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6.4.1.4 The most unfavourable load scenario for all relevant installation phases and conditions shall be
considered.
6.4.1.5 All loads and forced displacements which can influence the product shall be taken into account. For
each cross section or part of the system to be considered and for each possible mode of failure to be analysed,
all relevant combinations of loads which can act simultaneously shall be considered.
6.4.1.6 When considering the environmental design load the most unfavourable relevant combination, position
and direction of simultaneously acting environmental loads shall be used when documenting the integrity of
the system, see also DNV-OS-H102 Sec.4 C.
6.4.1.7 Any possible accidental loads shall be considered.
Guidance note:
Accidental loads are described in DNV-OS-F101 Sec.4 F and interference loads in Sec.4 E.
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6.4.2 Load effects
6.4.2.1 A load effect is the resulting cross sectional load due to the applied loads (e.g. weight, pressure, drag).
6.4.2.2 All loads and load effects occurring during the marine operation that could influence the operational
procedure, the design or the dimensioning of structures shall be analysed and considered in planning and
preparation for marine operations according to the principles in DNV-OS-H102 Sec.4 A. See also DNV-OSF101 Sec.4 G for further guidance.
6.4.2.3 The characteristic load effects from the different load categories are combined with the inclusion of
load effect factors to constitute the design load effect. See also [6.4.3].
6.4.2.4 Requirements for vessel motion analysis are given in DNV-OS-H102 Sec.4 B.
6.4.3 Limit states
6.4.3.1 All relevant limit states shall be considered during design for all relevant phases and conditions. See
DNV-OS-H102 Sec.5 A200 for limit state definition and for limit states to be considered in design.
6.4.3.2 The ULS condition b) in Table 4-4 in DNV-OS-F101 and the ULS condition in Table 5-2 in DNV-OSF201 should be considered whenever relevant in addition to the load combinations defined in DNV-OS-H102.
Guidance note:
The above requirement may be fulfilled by applying the load combinations in DNV-OS-H102, with a load factor of
1.1 on G and Q loads in ULS combination b).
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6.4.4 Failure modes
6.4.4.1 All relevant failure modes (for the installation/construction phase) shall be investigated. A failure
mode is relevant if it is considered possible and the anticipated consequence(s) of the failure cannot be
disregarded.
6.4.4.2 The relevant failure modes may be grouped according to their nature, either as global (total system) or
local (individual member) modes of failure, see DNV-OS-H102 Sec.2 C200.
Guidance note 1:
Reference to relevant standards describing potential failure modes for various types of products are indicated below.
Use of alternative recognized standards may be accepted;
— Submarine pipelines: DNV-OS-F101
— Dynamic risers: DNV-OS-F201
— Flexible pipe systems: ISO 13628-2 (API 17J) or ISO 13628-11 (API 17B)
— Umbilicals: ISO 13628-5 (API 17E)
— Subsea power cables: DNV-RP-J301
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Sec.6 Installation of pipelines, risers, cables and umbilicals – Page 48
Guidance note 2:
Flexible pipe systems can include flowlines, risers and/or jumpers. I.e. flexible pipes may be used for both static and
dynamic applications. A flexible dynamic pipe will normally be categorized as a dynamic riser.
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6.4.4.3 The allowable MBR (minimum bending radius) shall be defined for all relevant loads.
Guidance note:
The definition should include at least the following information:
— Tables/curves showing allowable bending (curvature) as a function of tension and pressure if applicable.
— All possible failure modes.
— Safety factor(s) included in the indicated MBR.
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6.5 Installation - General
6.5.1 General
6.5.1.1 General operational requirements are given in [2.10]. The requirements of this subsection are generally
applicable to installation of all products described in [6.1.1.1], regardless of installation method. Additional
requirements pertaining to specific installation methods/products are given in the Subsection [6.6].
6.5.2 Initiation
6.5.2.1 The initiation point shall be of adequate design and have sufficient structural capacity to resist the
initiation load in any possible direction.
Guidance note:
The characteristic initiation load should be calculated as the maximum characteristic functional (P & Q) load
multiplied with a factor not less than 1.5 to include dynamic (environmental) effects.
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6.5.2.2 Purpose made initiation points, such as piles or dead man anchors, shall be load tested to 1.5 times
maximum characteristic bottom tension (functional load) during start-up prior to commencement of lay
operation. The direction of pull during test shall reflect the actual conditions during initiation. Holding time
should be at least 15 minutes.
6.5.2.3 If a diverless latch/sheave type of initiation system is used, ROV monitoring of the sheave is imperative
throughout the whole initiation phase. Further, crossings between running wires and other wires, pipelines,
mooring equipment etc. shall be continuously monitored.
6.5.2.4 The initiation head structure should have means of preventing overturning caused by product rotation.
Structures with COG above pipeline centre shall be specially considered.
6.5.3 Laying
6.5.3.1 Crossings shall be prepared according to the findings from a risk assessment.
6.5.3.2 Requirements for anchor positioned lay vessel operations are given in DNV-OS-F101 Sec.10 D400.
6.5.3.3 If anchors are used for positioning of laying vessel, the anchor handling tugs shall keep the anchor
secured on deck when manoeuvring above pipelines and other subsea equipment.
6.5.3.4 Weather limitations for anchor handling tugs should be defined and taken into consideration when
planning lay operations.
6.5.3.5 Vessel lay operations using dynamically positioned vessels shall comply with the requirements in
DNV-OS-H203.
6.5.4 Lay monitoring
6.5.4.1 The lay configuration and loads shall be controlled in order to ensure that these are within established
design parameters during installation. The configuration and loads may be controlled by various means and
shall be clearly described including allowable ranges for the specific installation. Redundancy is required.
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Sec.6 Installation of pipelines, risers, cables and umbilicals – Page 49
Guidance note:
The lay configuration may be controlled by tension, stinger tip clearance and lay back distance/touch down
monitoring. Depending on the installation vessel and type of product, the preferred method can alter.
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6.5.4.2 The product touch down point shall be monitored as well as other interface points that are critical to
the integrity of the product or represent a risk for fixed installations or other subsea installations.
6.5.4.3 In order to enable continuous lay operations, adequate contingency measures for touch down
monitoring shall be established in case of primary monitoring system failure.
6.5.4.4 The ROV monitoring laying operations shall have sufficient working radii to observe critical areas
such as touchdown point, turning points etc. during laying. See also [2.9].
6.5.5 Lay-down
6.5.5.1 The laydown head structure should have means of preventing overturning caused by product rotation,
structures with their COG above the pipeline centre shall be specially considered.
Guidance note:
In cases where orientation of lay down head structure is not relevant for the preceding operations, this requirement
could be disregarded. The requirement in [6.5.5.3] will apply in this case.
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6.5.5.2 Laydown tools shall be designed to resist the maximum laydown forces from all radial directions in
case of pipe rotation or include an effective swivel system.
6.5.5.3 Laydown tools should have a release mechanism that can be operated even if landed upside down or
on their side.
6.5.6 Shore pull
6.5.6.1 The requirements of this subsection are applicable to the execution, inspection and testing of shore pull
when products as described in [6.1.1.1] are pulled either from a vessel onto the shore, or vice versa.
6.5.6.2 Detailed requirements for the execution, inspection and testing of shore pull shall be specified,
considering the nature of the particular installation site.
6.5.6.3 Measuring devices shall be used to control the integrity of the product during execution of the shore
pull. The product tension and pulling force shall be continuously monitored, and shall be kept within allowable
limits. Monitoring with ROVs can be needed.
6.5.6.4 The winches shall be equipped with wire tension and length indicators and recorders. All measuring
equipment shall be calibrated, and an adequate amount of spares shall be provided to ensure uninterrupted
operation.
6.5.6.5 It shall be documented that ROVs are able to operate under the seastate expected for the operation in
question. Factors such as water depth, visibility and effect of breaking waves should also be considered.
6.5.6.6 Satisfactory abrasion resistance of the product coating shall be demonstrated for the installation
conditions.
6.5.6.7 Buoyancy aids or pre-installed seabed rollers may be used to maintain pulling tension within allowable
limits.
6.5.6.8 Buoyancy aids shall be designed providing sufficient redundancy. The number and capacity of
buoyancy elements shall be sufficient to ensure that the product will stay afloat in case of damage to or loss of
a realistic number of elements.
6.5.6.9 If buoyancy elements are used, handling of buoyancy elements and control of product catenary are
normally controlled by light workboats. The limiting environmental conditions for these operations shall be
specified so that work carried out from small workboats is feasible and safe.
6.5.6.10 Visibility and adequate lightening shall enable full overview of the floating product.
6.5.6.11 Workboat crews should be especially instructed/trained in order to control and handle the product
without the risk of imposing damages
6.5.6.12 A shore pull / shore initiation operation will in most cases be a shallow water operation, which can
limit the ability of the installation vessel to position freely, and can also limit the use of thrusters due to draft
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Sec.6 Installation of pipelines, risers, cables and umbilicals – Page 50
limitations. The effect on the DP capacity and the system redundancy shall be carefully considered, to maintain
the required positioning capabilities.
6.5.6.13 Requirements and considerations related to design and preparation of landfall/onshore part of the
product system may be found in DNV-OS-F101, Submarine Pipeline Systems and in DNV-RP-J301 for Cable
Systems.
6.6 Product specific installation requirements
6.6.1 Pipeline system installation
6.6.1.1 The installation of submarine pipeline systems shall comply with the requirements in DNV-OS-F101
Sec.10 F.
6.6.2 Riser, umbilical and cable installation
6.6.2.1 Termination head transfer from storage position to tensioner system shall be done in a controlled
manner, special attention should be given to minimum bending radius (MBR) of the product and the axial
tension maintained during transfer. Dynamic behaviour (swinging) of heavy crane hooks etc. during handling
of product shall be specially considered.
6.6.2.2 Product handling should be considered step by step. Governing combinations of load directions and
magnitudes shall be identified and included in calculations.
6.6.2.3 Product handling on a vessel will imply that several tension systems are in operation at the same time
(winches, cranes, tensioner, friction forces etc.); this fact places special demands on the rigging design both
with regard to minimum breaking strength and load direction and distribution between the different parts of the
rigging.
6.6.2.4 The clearance to installation vessel (moonpool or vessel side) shall be monitored and maintained
during all phases of the installation. In case of small clearances between product and vessel, contact points shall
be provided with suitably radiused protection.
6.6.2.5 Laydown of product shall be engineered ensuring that the product can be abandoned without
compromising any parameters specified by the manufacturer. During project preparations, the product
abandonment and recovery arrangement shall be designed, including, for example, grappling lines for
recovery, marker buoys, etc.
6.6.2.6 Prior to planned abandonment of product, the ends shall be sufficiently protected from water ingress
so that the cable can be safely abandoned on and retrieved from the seabed.
6.6.2.7 Further recommendations to installation of subsea power cables may be found in DNV-RP-J301. The
recommendations in DNV-RP-J301 can also be applicable to other types of subsea cables such as fibre optic
cables.
6.6.3 J-tube pull-in of flexible risers, flexibles pipelines, umbilicals and cables
6.6.3.1 Prior to pull-in of products into J-tubes, the position of the J-tube, clamps, supports and product shall
be confirmed and evaluated with respect to assumptions made in the design. Potential damage shall be
identified and relevant measures taken if necessary.
6.6.3.2 To prevent the pulling head and product from jamming and to ensure that the J-tube is clear of debris
and obstructions, the diameter, roundness and cleanliness of the J-tubes shall be inspected by gauging pigs,
pulling a test pipe or similar.
6.6.3.3 The entry of the product into the bellmouth shall be continuously monitored, and the tension in the pullin cable shall be within specified limits.
6.6.3.4 Upon completion of the J-tube pull-in, a survey shall be performed to confirm the position of the
product including supports etc. Potential damage shall be identified and appropriate measures taken if required.
6.6.3.5 Any possible skew loads on pull-in heads associated with entry into the bellmouth, through bends etc.
shall be considered in the design.
6.6.3.6 Friction effects shall be calculated according to the principles in DNV-OS-H102 Sec.4 A600.
6.6.3.7 If lubricant is planned to be used during pull-in to reduce friction, the compatibility of the lubricant
with the surfaces in question both with respect to chemical reactions and friction reduction must be
documented. Testing may be carried out in order to establish applicable friction coefficients following the
principles in DNV-OS-H102 Sec.2 E400.
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Sec.6 Installation of pipelines, risers, cables and umbilicals – Page 51
6.6.4 Bundle and pipe string installation
6.6.4.1 In general, the forces and configuration for off bottom tow (slow speed tow of bundle close to seabed)
shall be accurately established in order to keep the full length of the bundle including structures clear of the
seabed. It is of great importance that load variations can be readily detected as this could indicate uncontrolled
contact with seabed/obstacles.
6.6.4.2 Bundle deflection due to side current shall be analysed for the characteristic current conditions in
approach and installation areas as well as the necessary pull force/catenary length to keep the bundle within the
corridor. When a bundle is moved in “off bottom tow mode” lateral friction between the ballast chain and the
seabed cannot be utilised for counteracting the lateral deflection.
6.6.4.3 Fatigue analysis shall be carried out to verify that fatigue ‘damage’ as a result of transport loads is
acceptable in relation to the total operating fatigue life of the bundle.
6.6.4.4 If a pull-in system is being using for the final bundle positioning, the necessary pull in force should be
calculated. Friction between seabed and bundle/ballast chain, general seabed topography, back tension, etc.
should be considered.
6.6.4.5 Ballast calculations shall be presented for the complete water filling/ballast operation. If the bundle is
pressurised prior to installation it shall be demonstrated that the bundle is stable during the bleed off to ambient
pressure and that weight loss due to escaping gas does not cause the bundle to ascend.
6.6.4.6 Crossings should be kept to a minimum; post flooding contact forces shall be determined for each case.
Potential chafing effects for pull in wires shall be evaluated.
6.6.5 Tie-in of pipe strings and bundles
6.6.5.1 It is assumed that integration tests, if applicable, have verified the operability of the various tools and
equipment. Test reports should highlight and reflect critical operational sequences and their limiting factors.
6.6.5.2 In general, procedures for the operational sequences listed below should be established, including
contingency plans, and limiting weather criteria:
—
—
—
—
—
—
—
pull in tool installation/retrieval
connection tool installation/retrieval
pull head disconnection/retrieval
connection of pull-in wire to pull-in head
guide wire installation
flooding of bundle
chain and buoyancy tank removal.
6.6.5.3 Suitable arrangements shall be provided for release of towing wire from pull head. Residual tension
and/or torsion should be considered.
6.7 Tie-in operations
6.7.1 Application
6.7.1.1 The requirements of this sub-section are applicable to subsea tie-in operations using mechanical
connectors. Tie-in operations above water and tie-in operations using welding are covered in DNV-OS-F101.
6.7.1.2 Tie-in operations by means of hot or cold taps are subject to special consideration and agreement.
6.7.2 General
6.7.2.1 The alignment and position of the tie-in ends shall be within the specified tolerances before completing
the tie-in.
6.7.2.2 During all handling, lifting and lowering into final position, open flange faces shall be protected against
mechanical damage.
6.7.2.3 Tie-in tool capabilities shall be sufficient to overcome forces from friction, soil build up, holdback and
misalignment.
6.7.2.4 Tie in tool capabilities shall be based on documented values achievable on site.
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Sec.7 Soil and foundations – Page 52
SECTION 7 SOIL AND FOUNDATIONS
7.1 Soil capacity and on bottom stability
7.1.1 General
7.1.1.1 Installation shall be planned to ensure that the object can be properly seated at the intended site without
excessive disturbance of the supporting soil.
7.1.1.2 It should be documented that during all phases of the installation operation the object remains stable
on the sea bed, without experiencing unacceptable displacements due to soil failure.
7.1.1.3 A general reference is made to DNV CN30.4 for selection of soil properties and determination of
foundation capacities.
7.1.2 Stability calculations
7.1.2.1 Whether the permanent foundation solution is based on mat foundation or piled foundation, there will
often be a temporary phase during installation where the object will be supported on mats, possibly equipped
with skirts.
7.1.2.2 Stability should be checked for load combinations including gravity loads, environmental loads where
significant, and any other loads applied to the structure during installation, e.g. during stabbing of piles.
7.1.2.3 For reasonably homogeneous soil conditions, stability may be checked using conventional bearing
capacity formulae, accounting for inclined loading combined with checks for pure sliding. Recommendations
for idealised soil conditions are given in DNV CN30.4 [4.4].
7.1.3 Material factors
7.1.3.1 For foundation failures which can have unacceptable consequences, such as structural damage or
irrecoverable, unacceptable displacements, material factors should be applied according to relevant design
standards, e.g. DNV CN30.4.
7.1.3.2 The adequacy of the normal load and material factors should be evaluated in relation to the proposed
installation procedure and governing boundary conditions.
Guidance note:
Provided that the installation is performed under controlled conditions by use of heave compensator, which effectively
prevents excessive impact velocity, standard safety factors can be used. Otherwise, adjustments should be agreed on
a case by case basis.
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7.2 Loads and installation aspects
7.2.1 Positioning loads
7.2.1.1 Forces due to horizontal and vertical impact velocity between the object and sea bed or bottom support
structure should always be evaluated from case to case and a maximum effective impact velocity should be
specified, which accounts for the boundary conditions in [7.2.2].
Guidance note:
In cases where the consequences of high impact velocity are documented to be minimal and insignificant the vertical
impact velocity can be determined based on other governing boundary conditions. The maximum vertical impact
velocity need not be taken greater than the free fall velocity of the object in calm water.
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7.2.1.2 Characteristic ULS positioning loads in vertical and horizontal direction should normally not be taken
less than 3% of the installed object's submerged weight including added mass.
7.2.2 Installation effects on the soil
7.2.2.1 To avoid risk of foundation failure during installation an impact analysis should be carried out.
Guidance note:
Subsea structures are often placed on the sea floor from an installation vessel. Vertical heave motions in combination
with the lowering velocity result in an impact between the sea floor and the structure. This impact is normally
controlled by limiting weather criteria and carefully planned, well controlled installation operations. Nonetheless,
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Sec.7 Soil and foundations – Page 53
subsea structures can and still do on occasion suffer foundation failure during installation, mainly in soft soil
conditions.
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7.2.2.2 Impact analysis should consider and establish relationships between the following factors:
—
—
—
—
—
—
—
—
submerged weight of object
tension in installation wire
flexibility of installation wire
heave motion
effective lowering velocity considering sensitivity of winch mechanism (slow running or star-up)
hydrodynamic (added) mass forces
water evacuation areas (for foundations with skirts)
governing soil properties.
Guidance note:
Impact analyses are described in DNV-RP-H103 Sec.6.
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7.2.2.3 Based on the impact analysis, the allowable maximum set-down velocity can be determined. In order
to control that the actual set-down velocity is less or equal, it will in most cases be necessary to use a heave
compensator, see [2.4], which controls and limits the heave motion prior to touch-down. Without heave
compensation, failure due to global displacement and/or local soil disturbance can occur. The consequences of
such incidents should be investigated.
7.2.2.4 When deciding upon allowable heave, the possible magnification of heave motions due to resonance
should be taken into account.
7.2.2.5 The possibility of snap loading in the lifting wire when the object is set on the seabed should be
considered. This should in particular be focused upon moderate water depths with correspondingly stiff lifting
wire and when the maximum heave velocities are higher than the crane lowering velocity. If the wire is not paid
out sufficiently once the lifted object is set on the seabed, the force in the wire due to snap loading will in most
circumstances be increased due to seabed suction.
7.2.2.6 Deceleration associated with impact induces additional dynamic forces on equipment and structural
elements which should be evaluated; this effect is most relevant when installing an object on hard ground.
7.2.3 Penetration and levelling of skirted foundations
7.2.3.1 The self-penetration of a skirted foundation should be estimated prior to installation operations.
7.2.3.2 When suction is required for obtaining full penetration of a skirted foundation the expected range of
suction should be based on expected range of penetration resistance. A maximum allowable suction should be
defined based on the concerns to avoid buckling of skirts and to avoid piping and soil heave inside the skirts
due to soil failure (reversed bearing capacity failure).
7.2.3.3 A structure supported by three or more skirted foundations may be levelled by application of suction
and/or overpressure. Procedures for levelling should be prepared in advance including limitations on the
allowable suction and overpressure.
7.2.3.4 The entire installation including penetration and levelling shall be monitored and reported. In case the
actual self-penetration or suction is outside the predicted range, a re-evaluation of the calculations made should
be performed. It can be necessary to re-evaluate the foundation design.
7.2.3.5 Recommendations for estimating and controlling penetration and levelling are given in DNV-RPH103 Sec.6.
7.3 Miscellaneous
7.3.1 Effects of conductor installation and shallow well drilling
7.3.1.1 Conductor installation and shallow well drilling require attention from a subsea structure integrity
point of view.
7.3.1.2 Planning for conductor installation should take into account the potential for disturbance of existing
foundation soils and the risk of reducing stability of the structure (or of adjacent conductors) further.
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Sec.7 Soil and foundations – Page 54
Guidance note:
— Soil disturbance during drilling operations can result from hydraulic fracture, washout (uncontrolled enlargement
of the drilled hole), or shallow gas pockets.
— Hydraulic fracture occurs where drilling fluid pressure is too high and fluid is lost into the formation.
— Washout generally occurs in granular soils and can, in part, be induced by high drilling fluid circulation rates or
drilling without mud. Washout can produce large voids in the soil structure and lead to stress relief in the
surrounding soils.
— When pumps are applied for disposal of drill mud the bore hole can collapse due to excessive suction.
— These incidents can be accompanied by loss of circulation of drilling fluids or in creation of sea floor craters.
Thereby the stability of foundations can be reduced and displacements increased. These detrimental effects can
occur whether the drilling takes place after installation of the structure or before, e.g. through a pre-installed
template or for an exploration well.
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7.3.1.3 In case of pre-drilled wells, records of conductor installation and shallow well drilling shall be
available to the designer of the structure. The cuttings from the well drilling operation, if allowed to accumulate
on the sea floor, should be taken into account both in the object installation and retrieval procedures.
7.3.2 Retrieval of object
7.3.2.1 If retrieval without overpressure (inside skirted foundations) or jetting is anticipated, the forces
anticipated during retrieval should be determined, to ensure that retrieval can be accomplished with available
means.
7.3.2.2 For re-positioning or retrieval of an object placed on the sea bed, forces due to suction should be
calculated. This may be done by using bearing capacity formulae as given in Classification Note 30.4 section
4.4. It should be noted that the pull-out resistance in cohesive (clay) soils will increase with increasing loading
rate (or pull-out velocity), which should be accounted for.
7.3.2.3 Retrieval forces are dependent on soil parameters, foundation geometry, lifting velocity, consolidation
time, contact pressure, etc.
7.3.2.4 Retrieval force calculations/analyses shall be carried out according to recognised methods, see DNVRP-H103 Sec.6.
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